AKCAKALE, Turkey (AP) Syrian government troops will deploy along the border with Turkey to help Kurdish fighters fend off Turkey's invasion of northern Syria, the Kurds said Sunday, hours after President Donald Trump ordered all U.S. troops to withdraw from the area to avoid getting caught in the middle of the fast-escalating conflict.

The announcement represents a major shift in alliances for Syria's Kurds after they were abandoned by the U.S., with whom they were longtime partners in the fight against the Islamic State group.

Adding to the turmoil, hundreds of Islamic State families and supporters escaped from a holding camp in northern Syria amid heavy clashes between Turkish forces and the Kurds.

The dizzying developments reflected the rapidly growing chaos that has unfolded in the week since Trump ordered U.S. forces in the region to step aside, clearing the way for the Turkish attack on the Kurdish fighters it considers terrorists.

Trump's decision has been broadly condemned at home and abroad by critics who accuse him of betraying the Kurds, who long fought alongside the U.S. to help defeat the Islamic State group in Syria.

U.S. Defense Secretary Mark Esper said all American troops will withdraw from northern Syria because of the increasing danger posed by the fighting.

"We have American forces likely caught between two opposing advancing armies, and it's a very untenable situation," he said on CBS' "Face the Nation." He did not say how many would withdraw or where they would go but that they represent most of the 1,000 U.S. troops in Syria.

The peril to American forces was illustrated on Friday, when a small number of U.S. troops came under Turkish artillery fire at an observation post in the north. No Americans were hurt. Esper said it was unclear whether that was an accident.

Trump, in a tweet, said: "Very smart not to be involved in the intense fighting along the Turkish Border, for a change. Those that mistakenly got us into the Middle East Wars are still pushing to fight. They have no idea what a bad decision they have made."

Meanwhile, Esper said the U.S. also has come to believe that the Kurds are attempting to "cut a deal" with the Syrian army and Russia to counter the invading Turks.

Shortly afterward, Kurdish officials announced they will work with the Syrian government to fend off the Turkish invasion, deploying side by side along the border. Syrian TV said government troops were moving to the north to confront the Turkish invasion but gave no details.

A Syrian Kurdish official and a war monitor also said Syrian government forces were poised to enter Kurdish-controlled towns from which U.S. troops are pulling out, following a deal reached through Russia.

The Syrian Observatory for Human Rights said the deal covered the towns of Kobani and Manbij. U.S. troops were deployed in the towns after they were cleared of Islamic State militants in 2015.

The Kurdish fighters had few options after the United States abandoned them, and it had been anticipated they would turn to the government of Syrian President Bashar Assad and its Russian allies for support.

The Syrian troop movements raise the risk of a clash between Syria and Turkey.

In addition, a return by Assad's forces to the region where Syrian Kurds have built up an autonomy in the north would be a major shift in Syria's long-running civil war, further cementing Assad's hold over the war-ravaged country.

It would also mean that U.S. troops no longer have presence in an area where Russia and Iranian-backed militias now have a role.

Turkey's official Anadolu news agency, meanwhile, said Turkey-backed Syrian forces have advanced into the center of a Syrian border town, Tal Abyad, on the fifth day of Turkey's offensive. Turkey's Defense Ministry tweeted that its forces had taken control of the main highway running between Hassakeh, a major town and logistics hub, and Ein Eissa, the administrative center of the Kurdish-held areas.

Casualties mounted. On Sunday, at least nine people, including five civilians, were killed in Turkish airstrikes on a convoy in the Syrian border town of Ras al-Ayn, according to the Observatory and Syrian Kurdish officials.

Images of the attack showed bodies and severed limbs strewn in the street. Some of those killed appeared to be carrying guns. Activists said the gunmen were guarding the convoy.

Turkish President Recep Tayyip Erdogan on Sunday ruled out any mediation in the dispute with the Kurds, saying Turkey won't negotiate with "terrorists." NATO member Turkey views the Syrian Kurdish fighters as terrorists because of their links to the Kurdish insurgency inside Turkey.

The fighting has raised fears that some of the thousands of Islamic State members and sympathizers held by the Kurds will escape or be released in the chaos, allowing the battered extremist group to make a comeback and sow terror at will.

On Sunday, heavy fighting reached a displaced-persons camp in Ein Eissa, some 35 kilometers (20 miles) south of the border, that is home to some 12,000 people, including around 1,000 wives and widows of Islamic State fighters and their children, held in a special detention area.

The Kurdish-led administration in northern Syria said in a statement that 950 IS supporters escaped after attacking guards and storming the gates. It was not immediately possible to confirm that figure.

"It gets worse by the hour," Esper said of the fighting. "These are all the exact things" that U.S. officials warned Erdogan would probably happen in urging him not to invade.

The United Nations said more than 130,000 Syrians have fled since the operation began last week. Turkey said 440 Kurdish fighters have been killed since the operation began Wednesday. The SDF said 56 of its fighters have died. Turkey also said four of its soldiers were killed, along with 16 allied Syrian fighters.

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El Deeb reported from Beirut. Associated Press writer Zeynep Bilginsoy in Istanbul contributed.