Members of Iran's Islamic Revolutionary Guards Corps (IRGC) are providing non-military assistance in Syria and Iran may get involved militarily if its closest ally comes under attack, commander-in-chief Mohammad Ali Jafari said on Sunday.
General Jafari's statement is the first official acknowledgment that Iran has a military presence on the ground in Syria where an 18-month-old uprising has left tens of thousands dead.
Western countries and Syrian opposition groups have long suspected Iran has troops in Syria. Iran has denied this.
"A number of members of the Qods force are present in Syria but this does not constitute a military presence," Iranian news agency ISNA quoted Gen. Jafari as saying at a news conference.
Qods is an IRGC unit set up to export Iran's ideology. It has been accused of plotting attacks inside Iraq since the overthrow of Saddam Hussein.
Gen. Jafari did not indicate how many IRGC members were in Syria but said they were providing "intellectual and advisory help".
The Islamic Republic has backed Syria's President Bashar al-Assad since the crisis began and regards his rule as a key part of its axis of resistance against Israel and Sunni Arab states.
Gen. Jafari also said Iran would change its policy and offer military backing if Syria came under attack.
"I say specifically that if Syria came under military attack, Iran would also give military support but it ... totally depends on the circumstances," he said.
U.S. officials this month accused Iraq of facilitating the transfer of weapons to Syria by opening its airspace to Iranian aircraft. Baghdad has denied the accusation.
Analysts say that losing its key Syrian ally would weaken the Islamic Republic's ability to threaten Israel through the Syrian-backed Shi'ite resistance movement Hezbollah.
Gen. Jafari dismissed Israel's threats of attack on Iran, saying Israel was having trouble persuading the United States to back its actions.
"Our answer to Israel is clear. In the face of such actions by the Zionist regime, nothing of Israel would remain," he said.
He said any Israeli attack on Iran would also trigger retaliatory action on U.S. bases in the region and that trade via the Strait of Hormuz would be disrupted.
An attack on Iran would also call into question Iran's commitment to the nuclear Non-Proliferation Treaty (NPT), he said, comments that will cause concern among Western diplomats who want to find a peaceful resolution to Iran's nuclear programme and avoid military consequences.
"If international organizations cannot stop Israel, Iran will not see itself as committed to its obligations. Of course this does not mean that we will go in the direction of a nuclear bomb," Gen. Jafari said.
Three rounds of talks earlier this year between Iran and the P5+1 group of countries – the United States, Russia, China, Germany, France and Britain – have so far failed to reach agreement on Iran's nuclear activities which the U.S. believes are targeted at developing a weapons capability.
The West is demanding that Tehran halts all high-grade enrichment, close its Fordo nuclear facility and ship out all stocks of high-grade uranium.
Tehran maintains its nuclear program is entirely peaceful.