Updated at 12 p.m. ET
Turkish forces began crossing the Syrian border on Wednesday, launching an operation in Kurdish-dominated areas of the country's north, President Recep Tayyip Erdogan announced.
The Turkish offensive jeopardizes Kurdish-led forces who have been a key U.S. ally in the bloody fight against ISIS. Turkey says those same forces are linked to militant groups who stage attacks in a separatist movement against the Turkish government.
Late Sunday, the White House abruptly announced it was pulling troops away from the border and that Turkey planned to launched an offensive — a major shift in U.S. policy that followed a phone call between President Trump and Erdogan. Senior officials have said they were not consulted or informed about the change.
The Turkish military is working with the Syrian National Army, Erdogan said, adding that the area they targeting Kurdish fighters as well as ISIS extremists.
"Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area," Erdogan said.
Ahead of the operation, Turkish soldiers used heavy equipment to remove a section of concrete border wall so that troops could cross, an official told Reuters.
A U.S. military official in Syria tells NPR's Tom Bowman that the Turkish airstrikes are "more expansive than shaping a limited incursion."
The U.S. is tracking people who are being displaced from the Syrian cities of Ras al-Ayn, Tal Abyad, Qamishli and Ain Issa, the official says, reflecting a span of some 140 miles along the north and northeastern border.
On Tuesday, Turkey reportedly struck the Syrian-Iraqi border to keep Kurdish forces from using it as a conduit to reinforce their positions, the news agency said.
Earlier, Islamic State militants reportedly carried out an attack on the city of Raqqa in northern Syria, including a post manned by U.S.-backed Kurdish-led fighters.
More than 3 million Syrian refugees are registered in Turkey, having fled brutal conditions imposed by both ISIS and their country's civil war. Erdogan said Wednesday that the long-anticipated offensive aims to establish "a safe zone, facilitating the return of Syrian refugees to their homes."
The operation is causing fear among the U.S.'s Kurdish allies. Mustafa Bali, a spokesperson for the Kurdish-led forces, said: "Turkish warplanes have started to carry out airstrikes on civilian areas. There is a huge panic among people of the region."
The White House decision to abandon posts along the border and give Turkey a free hand in taking on Kurdish groups has sparked a sharp bipartisan backlash in Washington.
Brett McGurk, who was Trump's special envoy for the fight against ISIS, also decried the decision in an interview with NPR.
"Presidents do a lot of things, but the most consequential are decisions of war and peace like this, and you can't make decisions on a haphazard basis after a single call with a foreign leader," McGurk said. "This is almost unprecedented."
Jens Stoltenberg, NATO's Secretary General, said via Twitter: "I count on Turkey to act with restraint & ensure that the gains we have made in the fight against ISIS are not jeopardised."
Human rights groups such as Amnesty International are also urging Turkey's military to act with restraint and ensure civilians' safety.
"Turkey has an obligation under international humanitarian law to take all possible measures to protect civilians and to ensure they have access to humanitarian aid," Amnesty International's Middle East Research Director Lynn Maalouf said in a statement. "Civilians wishing to flee the fighting must be given safe passage to do so."
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