The Turkish military has launched an operation to clear the Syrian border town of Jarablus of so-called Islamic State (IS) militants, officials say.
Turkish special forces inside Syria were supported by US-led coalition air strikes, the government said.
The operation comes as Syrian rebels backed by Turkey prepare to launch an assault on the town.
Turkey has vowed to “completely cleanse” IS militants from its border region.
It blames IS for a bomb attack that killed dozens of people in the south of the country at the weekend.
The Turkish army began shelling Jarablus at about 04:00 local time (01:00 GMT), the state-run Anadolu news agency said.
It had earlier ordered residents in the Turkish town of Karkamis – just across the border from Jarablus – to evacuate after the town was hit by IS mortar fire.
Turkey’s backing of a Syrian rebel assault on Jarablus, to be launched from its territory, is also seen as an attempt to prevent the town falling into the hands of Syrian Kurdish forces.
The Turkish military has also shelled positions belonging to the Kurdish YPG militia, apparently to deter them from taking Jarablus themselves.
Turkey views the YPG as an extension of the Kurdistan Workers Party (PKK), a Turkish-Kurdish rebel group fighting for autonomy since the 1980s.
However the YPG is backed by the US in the battle against IS and has been gaining territory in northern Syria. On Tuesday it took control of most of the northeastern Syrian town of Hassakeh.
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 Binali Yildirim acknowledged this week that he was one of the “actors” and suggested he could play a role in an interim leadership.