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 Turkish and US-led coalition air strikes, the government said.
The operation comes as Syrian rebels prepare to launch an assault on the town from Turkish territory.
Turkey has vowed to “completely cleanse” IS from its border region.
“The Turkish Armed Forces and the International Coalition Air Forces have launched a military operation aimed at clearing the district of Jarablus of the province of Aleppo from the terrorist organisation Daesh,” said a statement from the Turkish prime minister’s office, using another term for IS.
Turkey blames IS for a bomb attack that killed dozens of people in the south of the country at the weekend.
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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.
In recent days the Turkish military has 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.