The Turkish military returned fire after a mortar bomb fired from Syria landed in countryside in southern Turkey, the state-run Anatolian news agency reported the governor of Hatay province as saying on Friday.
Turkish artillery bombarded Syrian military targets on Wednesday and Thursday in response to shelling by Syrian forces that killed five Turkish civilians further east along the border.
Turkish Prime Minister Tayyip Erdogan warned on Friday his country was "not far" from war with Syria following cross-border attacks this week - words which highlighted the danger that the uprising against Syrian President Bashar Asaad will drag in its neighbors.
In a belligerent speech to a crowd in Istanbul, Erdogan warned the Assad government it would be making a fatal mistake if it picked a fight with Turkey.
The speech followed a Syrian mortar barrage on a town in southeast Turkey that killed five people on Tuesday.
Turkish artillery bombarded Syrian military targets on Wednesday and Thursday in response, killing several Syrian soldiers, and the Turkish parliament has authorized cross-border military action in the event of further aggression.
"We are not interested in war, but we're not far from it either," Erdogan said in his speech.
"Those who attempt to test Turkey's deterrence, its decisiveness, its capacity, I say here they are making a fatal mistake."
At the United Nations, the Security Council condemned the original Syrian attack and demanded that such violations of international law stop immediately.
The United States has said it stands by its NATO ally's right to defend itself against aggression spilling over from Syria's war.
The cross-border violence was the most serious so far in the conflict, now in its 19th month, and underscored how it could flare across the region.
Turkey, once an Assad ally and now a leading voice in calls for him to quit, shelters more than 90,000 Syrian refugees in camps on its territory and has allowed rebel army leaders sanctuary.
Violence has also spilled over into Lebanon.
'Air defense base captured'
More than 30,000 people have been killed in the revolt against Assad, which began with peaceful street protests but is now a full-scale civil war also fought on sectarian lines.
Across the country about 180 people were killed in violence on Thursday, including 48 government soldiers, the British-based Syrian Observatory for Human Rights said.
The rebels said they had captured an air defense base with a cache of missiles outside Damascus on Thursday, a boost to their campaign after a series of setbacks in the capital.
Video posted on YouTube of the aftermath of the assault showed dozens of rebels dressed in army fatigues celebrating as black smoke rose from a military installation behind them.
A middle-aged man holding a rifle says the attack was carried out by a rebel battalion from the town of Douma. It also showed rebels at a weapons cache which included what appeared to be part of a surface-to-air missile.
It was not possible to independently verify the videos. Access to Syria for foreign journalists is restricted by the Syrian government.
Although fighting often takes place in the Damascus suburbs, rebel forces have been unable to hold areas for long in the face of government artillery and air power. They have staged devastating bomb attacks on government and military offices in the heart of the city, however.
Syria apologizes
Syria's ally Russia said it had received assurances from Damascus that the strike on Turkey had been a tragic accident but Erdogan dismissed it, saying this was the eighth time Syrian mortar rounds had hit Turkish ground.
Turkey has made clear it is ready to launch retaliatory strikes again if the war spills over the border but it has also said it will act under international law and in coordination with other foreign powers.
Despite his belligerent rhetoric on Friday, Erdogan has said the parliamentary vote was a deterrent and he was not interested in war.
The UN condemnation was issued after two days of negotiations on an initial text rejected by Russia.
Consensus within the council on Syria-related matters is unusual and it has been deadlocked over the conflict, with veto-wielding Russia and China rejecting calls to sanction the Damascus government.