Syrian Kurds condemn the Turkish incursion into Islamic State-held Jarablus, calling it a "declaration of war."
"The Turkish intervention in Jarablus is a breach of Syria's sovereignty ... and a declaration of war on the [Kurdish] autonomous administration and federal system," Aldar Khalil, a member of the Kurdish Democratic Union Party (PYD), says.
In March, PYD and several allied groups declared a federal system of administration in northern Syria. The PYD's armed wing, the People's Protection Units (YPG), has been the main ally on the ground of the United States in its war against Islamic State. Turkey is opposed to Kurdish gains in northern Syria.
Turkey: Operation aimed against Islamic State
Turkish President Recep Tayyip Erdogan says operations began before dawn in Syria against Islamic State and the main Syrian Kurdish party, the Democratic Union Party (PYD), speaking live on television from an event in Ankara.
Erdogan says attacks from Syria must be stopped.
Turkish Foreign Minister Mevlut Cavusoglu later said the operation in Syria is aimed against Islamic State and that Kurdish forces there should support this goal.
He also insisted that Kurdish forces across the border need to retreat to the east of the Euphrates River or Turkey would do what is needed.
The Kurds are currently west of the water, having seized Minbij city this month from Islamic State. The Turkish operation is named Euphrates Shield.
United States: Kurdish forces in northern Syria were told they could not advance on Jarablus
The US will provide air cover and advisors for the Turkish military operation in Jarablus in north Syria, a senior US administration official says on board Vice President Joe Biden's plane heading to Ankara.
The official says Kurdish forces in northern Syria were told they could not advance on Jarablus. The official says Washington wants to avoid direct clashes between Turkey and the Syrian Kurds.
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The Syrian government says the Turkish operation in northern Syria is a "flagrant breach" of the country's sovereignty.
Turkish tanks crossed the border into Jarablus in northern Syria, state broadcaster TRT reported Wednesday citing military sources, while Syrian rebels forces told dpa they are also crossing into the Islamic State-held town from Turkey.
Turkish jets launched airstrikes against the northern Syrian town of Jarablus on Wednesday to clear it of Islamic State militants, state media reported saying it was a joint operation with the US-led coalition.