Air strikes shook the Damascus area early Sunday in what Syria said was an Israeli bombing, the second airborne attack on targets in Syria in three days and a further escalation of Israel's response to the Syrian civil war.
The attack, following a similar strike Friday, raised fresh concerns about a spillover of the Syrian conflict into neighbouring countries, even as the United States weighs intervention following reports of use of chemical weapons in the fighting.
Israeli officials, who have vowed to stop the transfer of advanced weapons from Syria to Islamist militants, were silent about the latest strikes and reports that they targeted stocks of Iranian-made guided missiles destined for the Hezbollah group in Lebanon.
Syrian Deputy Foreign Minister Faisal Mekdad, interviewed by CNN, called the air strikes a "declaration of war" by Israel, while Syrian Information Minister Omran al-Zoabi warned they would have "dangerous" implications for the region. But he stopped short of a specific threat of retaliation.
The Israeli silence, which analysts said was meant to avoid goading Syria into a response, seemed part of a government assessment that the attacks would not ignite a broader conflict. Commentators said that the government had taken the calculated risk that the air strikes would not draw retaliation from the embattled Syrian leadership.
Amos Yadlin, a former chief of military intelligence who heads the Institute for National Security Studies in Tel Aviv, told Army Radio that Syria risked serious damage to its already battered military capabilities should it chose to respond against Israel.
"Assad knows that the rebels have made him the primary target, and if he tries to deflect the fire toward Israel, chances are that he will be attacked by both the rebels and Israel," Mr. Yadlin said. "The regime knows … that a confrontation with Israel today will put it in far greater peril."
The bombings, which according to reports from Syria hit multiple sites, underlined Israel's concerns that the upheaval in Syria could lead to a loss of control of chemical weapons and sophisticated arms.
Israeli officials say they are concerned that a possible breakup of Syria could shift an array of advanced weapons to Lebanon, making it the main focus of potential confrontation with Hezbollah, which is heavily backed by Iran.
The group is reported to have sent fighters to help support Syrian government forces, and Israeli experts monitoring the organization say that it is seeking to shift weaponry stored in Syria to Lebanon.
The attacks targeted stocks of Fateh-110 missiles, which have precision guidance systems more accurate than any missiles Hezbollah is known to possess, according to a Western intelligence official in the Middle East cited by the Associated Press.
A short-range ballistic missile developed by Iran, the Fateh-110 was upgraded in 2012 to improve its accuracy and increase its range to 300 kilometres.
Commentators said that Israel viewed such weaponry, which can reach key targets deep in Israeli territory, as a "game changer" in the hands of Hezbollah, which fired thousands of rockets into Israel in a war in 2006.
President Barack Obama, speaking on Saturday before the latest raids, said that it was up to Israel to confirm or deny any reports of an attack, but that Washington co-ordinates very closely with Israel. "The Israelis, justifiably, have to guard against the transfer of advanced weaponry to terrorist organizations like Hezbollah," Mr. Obama told the Spanish-language TV station Telemundo.
Israeli Prime Minister Benjamin Netanyahu pointedly avoided any mention of Sunday's attack in public remarks at the start of the weekly meeting of his cabinet.
But in an earlier ceremony inaugurating a road interchange named for his late father, Mr. Netanyahu said that "he taught me the enormous responsibility that we have to ensure the security of the State of Israel."
Despite the prevalent assessment in Israel that the air strikes would not trigger broader hostilities, the army protectively positioned two of its Iron Dome anti-missile batteries in northern Israel and domestic flights were cancelled in the area.
Mr. Netanyahu left as planned for a visit to China, but delayed his departure in order to meet with his security cabinet.
After the air strikes, Syria's state news agency SANA reported that explosions went off at the Jamraya military and scientific research centre northwest of Damascus, saying that "initial reports point to these explosions being a result of Israeli missiles." SANA said there were casualties but did not give a number.
Jamraya, about 15 kilometres from the Lebanese border, was hit in a previous Israeli strike in January, which was said to have targeted trucks carrying sophisticated anti-aircraft missiles believed to be headed for Hezbollah.
Syrian witnesses told news agencies that sites at Qasioun mountain overlooking Damascus were also hit in Sunday's strikes, and video footage taken by residents showed massive fiery explosions on the ridge. "Night turned into day," one man told Reuters from his home at Hameh, near the Jamraya facility.
In a letter to the United Nations Security Council, the Syrian Foreign Ministry protested what it called "Israeli aggression" which it said killed and wounded several people and "caused widespread destruction." The attack was also condemned by the Arab League.
In Tehran, Iran's Foreign Ministry spokesman Ramin Mehmanparast denounced the Israeli strike and urged countries in the region to remain united against Israel, according to the semiofficial Fars news agency.
Iranian Defense Minister Ahmad Vahidi was quoted by the ISNA news agency as saying that the Israeli attack, " which occurred with the U.S.'s green light, revealed the relationship between Israel and "the mercenary terrorists and their supporters," a reference to the Syrian rebels.
Mr. Yadlin, the former Israeli intelligence chief, said that the air strikes were a signal to Iran, making clear to Tehran that "when at least some of the players define red lines, and they are crossed, they take it seriously."
Netanyahu has urged the United States and other nations to set a "red line" for Iran's nuclear program, after which it could face military strikes on facilities that Israel says are developing elements of a nuclear weapon.
A look at the reasons for and possible implications of the escalation of Israel's involvement in Syria's civil war
Israel has said repeatedly it does not want to get dragged into Syria's civil war but has also warned that it will not allow so-called "game-changing" sophisticated weapons to flow across the border to Lebanon's Hezbollah, an Islamic militant group allied with the Syrian regime.
Israeli defence officials believe Iran has stepped up shipments of weapons to Hezbollah through Syria, including accurate longer-range Iranian missiles, as President Bashar al-Assad's position weakens. This could help explain the back-to-back Israeli strikes on Friday and Sunday on alleged Hezbollah-bound weapons in Syria. Before this week, Israel aircraft had struck Syria only once, in January.
Analyst Paul Salem of the Carnegie Middle East Center in Beirut says Israel may simply be sending a stern warning to deter such weapons smuggling. Salem says Israel also appears to be increasingly concerned about Iranian and Hezbollah forces fighting alongside Assad's troops, close to Israel's borders.
What is the U.S. view?
White House spokesman Josh Earnest said Sunday that "Israelis are justifiably concerned about the threat posed by Hezbollah obtaining advanced weapons systems, including some long-range missiles."
President Barack Obama said the U.S. co-ordinates closely with Israel, implying that Washington was not taken by surprise by the Israeli strikes.
The U.S. has long resisted getting involved in the conflict amid concerns that foreign weapons could end up in the hands of al-Qaida-linked groups or other extremists fighting with the rebels. However, Defence Secretary Chuck Hagel said recently that Washington is reviewing its opposition to arming the opposition.
The Israeli strikes illustrate that Obama and Israeli Prime Minister Benjamin Netanyahu have drawn different red lines in Syria's conflict.
Israel's main concern is that Hezbollah could obtain advanced weapons.
Obama has warned that the use of chemical weapons by the regime could have "enormous consequences." There have been some indications of chemical weapons use, but Obama has said he needs more definitive proof before making a decision about how to respond.
Could this escalate into a wider Mideast war?
Israel, which commands the region's most powerful military, appears to be taking a calculated risk that Syria, Hezbollah or Iran won't retaliate for its air raids. If the trio was to do so, it would mean opening up a new front at a time when it is fighting for the Assad regime's survival. Hezbollah also risks losing its position as the dominant military and political power in Lebanon, something it painstakingly rebuilt after the 2006 war, if Israel were dragged in to the conflict.
The initial Syrian response to Israel's airstrike early Sunday appeared relatively muted. Syria's government called the attacks a "flagrant violation of international law" and warned it has the right "to defend its people by all available means."
Still, Israeli officials have signalled Israel will not stop blocking weapons shipments to Hezbollah, raising the possibility of more Israeli airstrikes and a further escalation. Salman Shaikh of the Brookings Doha Center in Qatar says the Assad regime, Hezbollah and Iran increasingly view the Syria conflict as a zero-sum game.
What is Iran's role?
Iran is the senior partner in the axis since it supports the Assad regime and Hezbollah with weapons, though it's not clear how much tactical sway is being exerted by Tehran.
Advisers from Iran's Revolutionary Guard are believed to have longtime roles in Hezbollah's militia forces and Assad's army – serving as both point men for Tehran's aid and liaisons with the ruling clerics in Tehran. Yet Iran also keeps a distance from the actual battlefield.
Gen. Masoud Jazayeri, assistant to the Iranian chief-of-staff, told Iran's state-run Arabic-language Al-Alam TV on Sunday that Tehran "will not allow the enemy (Israel) to harm the security of the region" and that "the resistance will retaliate against the Israeli aggression against Syria."
Iran would, though, have a major say in any decision to retaliate for the airstrikes but is not believed to have an appetite for a confrontation with Israel. While Iran is fighting for regional influence and has often used its anti-Israel stance to do so, it has never attacked the Jewish state.
Will the Israeli strikes change the course of Syria's civil war?
The uprising against Assad erupted in March 2011 and quickly evolved into a civil war, leaving tens of thousands dead and millions displaced. Assad and those trying to topple him remain locked in a battlefield stalemate, with neither side able to deliver a decisive blow.
The rebels are dominated by Syria's Sunni Muslim majority, while Assad is a member of the Alawite sect, an offshoot of Shiite Islam. He as rallied hardcore supporters around him, including members of Syria's ethnic and religious minorities who prefer the current regime to Sunni majority rule.
During four decades of rule, President Bashar al-Assad and his father and predecessor, Hafez, used Syria's staunchly anti-Israel positions as a source of legitimacy even though both men kept Syria's frontier with the Jewish state quiet. Syria's civil war has increasingly eroded Mr. al-Assad's anti-Israel "credentials," after the regime attacked Palestinian refugee camps in Syria and the Palestinian militant group Hamas, made up of Sunnis, broke with the regime because of its crackdown on the rebels.
If Mr. al-Assad does not retaliate for the latest Israeli strikes, his claims to anti-Israel militancy would become even more tenuous. In an attempt to deflect attention, Syrian government officials on Sunday tried to portray the Syrian opposition as engaged in a common cause with Israel.
Future Israeli air attacks could also wipe out key Syrian military installations. Rebel forces have managed to seized captured a number of Syrian military bases, seizing heavier weapons but have advanced only slowly because of the regime's air superiority.
– Associated Press