Turkey returned fire after mortar bombs shot from Syria landed in a field in southern Turkey on Saturday, the day after Prime Minister Tayyip Erdogan warned Damascus Turkey would not shy away from war if provoked.
It was the fourth day of Turkish strikes in retaliation for mortar bombs and shelling by Syrian forces that killed five Turkish civilians further east on Wednesday.
The strikes and counter-strikes are the most serious cross-border violence in Syria's conflict, which began as a democracy uprising but has evolved into a civil war with sectarian overtones. They highlight how the crisis could destabilise the region.
NATO-member Turkey was once an ally of Syrian President Bashar al-Assad but turned against him after his violent response to an uprising in which more than 30,000 people have died, according to the United Nations.
Turkey has nearly 100,000 Syrian refugees in camps on its territory, has allowed rebel leaders sanctuary and has led calls for Mr. al-Assad to quit. Its armed forces are far larger than Syria's.
Mr. Erdogan said on Friday his country did not want war but warned Syria not to make a "fatal mistake" by testing its resolve. Damascus has said its fire hit Turkey accidentally.
Foreign Minister Ahmet Davutoglu struck a more defensive tone on Saturday, saying parliament's authorization of possible cross-border military action was designed as a deterrent.
"With the mandate we did not take a step towards war, we showed the Syrian administration our deterrence, making the necessary warning to prevent a war," he said.
"From now on, if there is an attack on Turkey it will be silenced," he said in an interview with state broadcaster TRT.
Mr. Davutoglu said international mediator on Syria Lakhdar Brahimi would come to Turkey before Russian President Vladimir Putin visits Ankara within the next ten days.
Arab League chief Nabil Elaraby described Mr. Brahimi's Syria mission as "virtually impossible", in an interview with Egyptian paper al-Ahram.
Asked about the efforts of the Egypt-Saudi-Turkey-Iran quartet to solve the Syrian crisis, Mr. Elaraby said: "The solution must comprise Iran. The important thing is that matters get moving."
Two rounds fired from Syria struck near Guvecci village in Yayladagi on Saturday, the Hatay governor's office said. It said the fire appeared to have been aimed by Syrian government forces at rebels along the border. There were no casualties.
The first round landed 50 metres inside Turkey at 7 a.m. (0400 GMT) and the Guvecci border post retaliated with four rounds from 81 mm mortars. It fired two further rounds after the second mortar struck around 11:30 a.m. (0830 GMT).
The governor's office warned people in the area not to go out on balconies or spend time in open places, Dogan news agency said. It said the Red Crescent was offering psychological support to people in the area.
There were two similar incidents in Hatay on Friday, when Mr. Erdogan issued his warning.
"Those who attempt to test Turkey's deterrence, its decisiveness, its capacity, I say here they are making a fatal mistake," he said in a bellicose speech to a crowd in Istanbul.
"We are not interested in war, but we're not far from war either. This nation has come to where it is today having gone through intercontinental wars," he said.
Turkish artillery bombarded Syrian military targets on Wednesday and Thursday, killing several Syrian soldiers after Syria's initial fatal bombardment. The United Nations Security Council condemned the original Syrian attack and demanded that such violations of international law stop immediately.
Russia, a staunch ally of Syria, has said it received assurances from Damascus that the strike on Turkey was a tragic accident but Mr. Erdogan dismissed them, saying Syrian fire had repeatedly hit Turkish soil.
Wednesday's Syrian strike on the town of Akcakale was of a different magnitude to previous incidents over the past 10 days, a Turkish government official told Reuters.
"Wednesday was different. There were five or six rounds into the same place. That's why we responded a couple of times, to warn and deter. To tell the (Syrian) military to leave. We think they've got the message and have pulled back from the area."
Syria has since ordered its warplanes and helicopters not to enter an area within 10 kilometres of the Turkish border and told its artillery units not to fire shells in areas close to the border, according to Turkish broadcaster NTV.
Syrian authorities have not confirmed this.
The Turkish General Staff on Saturday sought to quell concerns about scenes of people apparently crossing freely back and forth across the frontier in the Akcakale area.
"There are no uncontrolled or illegal transits along the border. The region which we are responsible for is completely under control," the General Staff said in a statement to state-run Anatolian news agency.
The United States has said it stands by its NATO ally's right to defend itself against aggression spilling over from Syria's war, while Russia appealed to Turkey to stay calm and avoid any action that could increase tensions.
The West has shown little appetite for the kind of NATO intervention that helped topple Libya's Moammar Gadhafi. Turkish calls for a safe zone in Syria would require a no-fly zone that NATO states are unwilling to police.
The 18-month-old Syrian revolt increasingly pits a Sunni Muslim opposition against Assad's Alawite minority.
U.S. President Barack Obama refuses to arm the rebels, partly out of fear that some of those fighting the Iranian-backed Assad are Islamist radicals equally hostle to the West.
Rebel forces are riven by divisions but Syrian government forces appear to lack the numbers to land a knockout blow and permanently hold rebel areas.
Rebels said they captured an air defence base with a cache of missiles outside Damascus on Thursday, a boost to their campaign after a series of setbacks in the capital.