Turkey has ordered residents in the town of Karkamis to evacuate after it was hit by mortars from so-called Islamic State militants in Syria.
Karkamis lies just across the border from Jarablus, an IS-held town which Turkish-backed rebels are expected to try to capture in the coming days.
A rebel force is massed in the area and preparing the offensive.
Turkey blames IS for a bomb attack that killed dozens of people in the south of the country at the weekend.
It says the group must now be cleared from the border region, and has been bombarding targets across the border in northern Syria ahead of an expected ground attack.
Turkey's increasing entanglement in Syria's war has added to the strain on its administration and security services following an attempted coup in mid-July.
It accused Fethullah Gulen of masterminding the attempted overthrow from his US home and has dismissed or detained thousands of the cleric's alleged followers. Mr Gulen denies any involvement.
On Tuesday, US officials confirmed they had received an extradition request for the cleric - and but they said it was on grounds of alleged crimes unrelated to the coup bid, though they did not clarify.
The BBC's Mark Lowen says the decision to evacuate Karkamis is not necessarily a sign that a ground operation is imminent, but a response to the shelling by jihadists.
The evacuation order came by loudspeaker, and minibuses were sent in to transport those without cars, he says.
As well as IS forces, Turkey has shelled Syrian Kurdish forces nearby, apparently to deter them from taking Jarablus themselves.
Fifty-four people were killed when the southern city of Gaziantep was hit by a suicide bombing on Saturday.
Our correspondent says the attack on a wedding in the city, blamed on IS, may have been spurred by reports of the imminent Syrian rebel offensive.
More victims of the blast are being identified and our correspondent says the wave of bombings in Turkey could intensify as the country becomes ever more embroiled in the Syrian war.
Why is Turkey shelling both IS and the Kurds?
Turkish Foreign Minister Mevlut Cavusoglu has said that IS should be "completely cleansed" from areas in northern Syria near its border.
Turkish forces have been exchanging shellfire with IS positions in the Jarablus area since Monday.
However, Turkey is also wary of moves that might bolster Syrian Kurdish forces, known as the YPG, which it views as an extension of the Kurdistan Workers Party (PKK), a Turkish-Kurdish rebel group fighting for autonomy since the 1980s.
On Monday, Turkey shelled YPG positions near Manbij, a town they took from IS this month.
The 1,500 fighters poised to enter Syria from Gaziantep are believed to be Turkish-backed Syrian rebels. A senior rebel official quoted by Reuters said they were fighting under the banner of the Free Syrian Army.
How the wedding attack in Gaziantep is connected
The identity and motive of the suicide bomber who attacked the wedding party have yet to be revealed.
Soon after the attack, President Recep Tayyip Erdogan said IS was the likely perpetrator but Prime Minister Binali Yildirim said on Monday that investigators actually did "not have a clue".
He downplayed earlier reports that the attacker was between 12 and 14 years old, saying this could not be confirmed.
The pro-Kurdish Peoples' Democratic Party (HDP) said the wedding was for one of its members, and IS have targeted Turkish Kurds in the past.
Many of the victims were children - the two youngest were four years old.
Sixty-six people are still in hospital, 14 of them in a serious condition, Turkey's Dogan news agency reported.
A disproportionately large number of women and children were killed in the attack because it targeted henna night, a part of the celebration attended mainly by women and children, says BBC Monitoring's Turkey analyst Pinar Sevinclidir.
Where is Assad in all this?
Syrian government forces are not directly involved in the battle for the border at Jarablus, having gradually lost ground in the north over more than five years of civil war.
Turkey's long-time position has been that President Bashar al-Assad must be ousted as a condition for peace in Syria.
However, Prime Minister Yildirim acknowledged this week that he was one of the "actors" and suggested he could play a role in an interim leadership.