Turkey's military has returned fire across the border after a Syrian mortar round again landed on Turkish soil, television channels say.
The incident happened in southern Hatay province on Friday afternoon, Turkish media said. No injuries were reported.
On Wednesday Syrian mortar fire killed five Turkish civilians in the town of Akcakale.
That prompted Turkey to return fire and its parliament to authorise military action inside Syria.
Prime Minister Recep Tayyip Erdogan had warned Syria earlier on Friday at a large rally in Istanbul that the countries were "not far" from war.
Although he has insisted the parliamentary vote was only a deterrent and that Turkey would not start a war, he said at the rally: "Those who attempt to test Turkey's deterrence, its decisiveness, its capacity, I say here they are making a fatal mistake."
On Friday, Turkey moved tanks and anti-aircraft missiles into Akcakale and a Turkish foreign ministry official told Associated Press that Syria had pulled tanks and other material away from the border.
Turkish NTV channel said Syria had ordered warplanes and helicopters not to enter within 10km (six miles) of the Turkish border, but Damascus has made no comment on this.
'We did not sleep'
Friday's shelling incident reportedly took place near the Turkish town of Altinozu in Hatay province, much further west, at about 16:30 GMT.
The governor of Hatay province, Celalettin Lekesiz, was quoted by the Anadolu agency as saying that Turkish troops "responded with fire" after a mortar round landed in a rural area.
Although there were no reports of fresh cross-border clashes in Akcakale, the situation there remains tense.
One resident of Oncul, close to Akcakale, told AP: "Our store owners, our citizens and our children are all very concerned. We did not sleep until morning."
On Thursday, the UN Security Council said the Akcakale shelling - which is believed to have been an accident - underscored the grave impact the Syrian crisis was having on "regional peace and stability". Two women and three children were killed.
Turkey's parliamentary vote authorised troops to launch cross-border operations against Syria and strike at Syrian targets for a period of one year.
Turkey's retaliatory fire is its first since the uprising against President Bashar al-Assad's government began 18 months ago.
Clashes between government forces and rebels continued across Syria on Friday.
The city of Homs was subjected to its most severe bombardment in five months, activists said.
They also reported fierce clashes in the second city Aleppo, and government shelling in the capital Damascus, Hama and Idlib.
Activists also posted videos online which they said showed a military aircraft being shot down by rebel fighters as it bombarded towns in the eastern Ghouta area.
It was unclear whether it was a helicopter or fighter jet.
According to activists, more than 30,000 people have been killed since the uprising against President Assad began. The UN estimates that at least 20,000 have died.