Turkey has launched its military operation in northern Syria, with explosions being reported in the town of Ras al Ain.
Turkish president Tayyip Recep Erdogan confirmed his military had begun its offensive, which follows a White House announcement on Monday that US armed forces would pull out of the region “soon”.
The White House said the decision was made on Sunday evening following a phone call between President Donald Trump and Mr Erdogan.
Since then, about 1,000 US troops have begun to move out of northeast Syria, leaving their allies, the Kurdish-led Syrian Defence Force (SDF) – seen as enemies of Turkey for the past 35 years.
On Tuesday, Turkish officials said its military had struck the Syrian-Iraqi border to prevent Kurdish forces using the route to reinforce the region.
President Erdogan’s aide, Fahrettin Altun, said fighters from the Kurdish YPG – viewed as terrorists by Turkey – could either defect or Ankara would have to “stop them from disrupting” Turkey’s struggle against Islamic State militants.
“The Turkish military, together with the Free Syrian Army, will cross the Turkish-Syrian border shortly,” Mr Altun tweeted.
“Turkey has no ambition in northeastern Syria except to neutralise a long-standing threat against Turkish citizens and to liberate the local population from the yoke of armed thugs,” he added in a Washington Post column.
The SDF has called the US decision a “stab in the back” and said they might start talks with the Syrian government and Russia to fill the vacuum left by a possible full US withdrawal.
Mr Trump’s decision to withdraw troops from northeast Syria has drawn criticism from both Republicans and Democrats who have warned for months that could lead to a massacre of the Kurds.
It has also rattled allies, including France, one of Washington’s main partners int he US-led coalition fighting IS.
Russia, Syrian President Bashar al-Assad’s strongest foreign ally, said Washington or Ankara did not tell them in advance about any agreements to pull out US troops.