AKCAKALE, Turkey (AP) — Turkish forces faced fierce resistance from U.S.-allied Syrian Kurdish fighters on the third day of Ankara's offensive in northern Syria, as casualties mounted, international criticism of the campaign intensified and estimates put the number of those who fled the violence at 100,000.
Later Friday, an explosion was reported in northern Syria near an outpost where U.S. troops are located, but none of the Americans were hurt, according to a U.S. official and a Syria war monitor. It was unclear whether it was from artillery or an airstrike, and it was the first time a coalition base was in the line of fire since Turkey's offensive began.
Turkey said it captured more Kurdish-held villages in the border region, while a hospital in a Syrian town was abandoned and a camp of 4,000 displaced residents about 12 kilometers (7 miles) from the frontier was evacuated after artillery shells landed nearby.
Reflecting international fears that Turkey's offensive could revive the Islamic State group, two car bombs exploded outside a restaurant in the Kurdish-controlled urban center of Qamishli, killing three people, and the extremists claimed responsibility. The city also was heavily shelled by Turkish forces.
Kurdish fighters waged intense battles against advancing Turkish troops that sought to take control of two major towns along the Turkish-Syrian border, a war monitor said.
The U.N. estimated the number of displaced at 100,000 since Wednesday, saying that markets, schools and clinics also were closed. Aid agencies have warned of a humanitarian crisis, with nearly a half-million people at risk in northeastern Syria.
On Sunday, U.S. President Donald Trump cleared the way for Turkey's air and ground invasion after he announced his decision to pull American troops from their positions near the border, drawing swift bipartisan criticism that he was endangering regional stability and putting at risk the lives of Syrian Kurdish allies who brought down the Islamic State group in Syria.
Trump had said at the time that the estimated 1,000 U.S. troops were not in harm's way from the Turkish offensive. Rami Abdurrahman, head of the war monitor Syrian Observatory for Human Rights, said the U.S. base was on a hill near the Kurdish-held town of Kobani, which had come under heavy Turkish fire.
U.S. Defense Secretary Mark Esper said Washington is "greatly disappointed" by the offensive, which has badly damaged already frayed relations with NATO-ally Turkey. In a strong statement of support for the Kurds, Esper insisted that "we are not abandoning our Kurdish partner forces, and U.S. troops remain with them in other parts of Syria."
Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, emphasized that U.S. forces are still working with Kurdish fighters.
U.S. troops conducted a military patrol about 30 kilometers (19 miles) south of Tal Abyad, in their first visible deployment since Turkey launched the operation. A U.S. official said, speaking on condition of anonymity to brief reporters, said the patrol was not in support of operations against the Turkish offensive.
Video showed five armored personnel carriers moving from west of Ein Issa in the direction of Tal Abyad, and the U.S. official said they avoid areas where active combat operations were taking place.
Despite the criticism, Turkish President Recep Tayyip Erdogan said his country "will not take a step back" from its offensive.
"We will never stop this step. We will not stop no matter what anyone says," he said in a speech Friday.
Plumes of black smoke billowed Friday from the Syrian border town of Tal Abyad as Turkey continued bombarding the area in an offensive that was progressing "successfully as planned," the Turkish Defense Ministry said.
Turkish troops and their allied Syrian opposition forces have advanced up to 8 kilometers (5 miles) into Syrian territory, Turkish Vice President Fuat Oktay told TRT World television. Turkey has said the military intends to move 30 kilometers (19 miles) into Syria and that its operation will last until all "terrorists are neutralized."
Turkey considers the Syrian Kurdish fighters to be terrorists linked to a Kurdish insurgency inside Turkey and says the offensive is a counterterrorism operation necessary for its own national security.
The Turkish Defense Ministry said four of its soldiers have been killed since Wednesday, with three wounded. Defense Minister Hulusi Akar said 342 "terrorists" — Ankara's term for Syrian Kurdish militiamen — have been killed so far. The figure could not be independently verified.
The Kurdish-led force said 22 of its fighters were killed since Wednesday.
The Kurdish militia has fired dozens of mortars into Turkey in the past two days, including Akcakale, according to officials in two provinces on the Turkish side. They said at least 17 civilians were killed in the shelling, including a 9-month-old boy and three girls under 15.
Mourners in Akcakale carried the coffin of the slain boy, Mohammed Omar Saar, as many shouted, "Damn the PKK!" referring to the Kurdish insurgent group in Turkey linked to Syrian Kurdish fighters. The PKK is considered a terrorist group by Turkey, the United States and other countries.
One attack hit the town of Suruc, and a child in the town of Ceylanpinar died of his wounds Thursday night, the Anadolu Agency reported.
On the Syrian side, seven civilians have been killed since Wednesday, activists said.
Russian President Vladimir Putin said he doubted the Turkish army has enough resources to take control of prison camps in the region housing Islamic State detainees, and he fears the captured fighters "could just run away," leading to a revival of the militant group.
"We have to be aware of this and mobilize the resources of our intelligence to undercut this emerging tangible threat," Putin said during a visit to Turkmenistan.
The Syrian Kurdish forces had been holding more than 10,000 IS members, but they said they are being forced to abandon some of those positions to fight the Turkish invasion.
Separately, NATO Secretary General Jens Stoltenberg urged Ankara to exercise restraint, although he acknowledged what he said was Turkey's legitimate security concerns about the Syrian Kurdish fighters.
In a news conference with Turkish Foreign Minister Mevlut Cavusoglu, Stoltenberg also expressed concern that the offensive could jeopardize gains made against IS. Cavusoglu said Turkey expected solidarity from its allies.
"It is not enough to say you understand Turkey's legitimate concerns; we want to see this solidarity in a clear way," he said.
European Union Council chief Donald Tusk expressed "grave concern" about the operation. Abandoning the Kurdish forces who have been crucial in fighting IS "is not only a bad idea" but raises questions "both of a strategic and moral nature," he said.
Tusk said a threat by Erdogan to let Syrian refugees flood into Europe was "totally out of place," adding that the EU will never accept "that refugees are weaponized and used to blackmail us."
Amélie de Montchalin, the French secretary for European affairs, said sanctions against Turkey will be "on the table" at next week's European Union summit, telling France Inter radio that Europe should respond to what she called a shocking situation. European diplomats in Brussels have responded cautiously to the idea of sanctions, even though Turkey's actions have brought near-unanimous criticism.
The White House also put Turkey on notice it could face new "powerful sanctions" and that the U.S. will "shut down the Turkish economy" if Ankara goes too far, with U.S. Treasury Secretary Steven Mnuchin saying Washington hopes it will not have to use its new, expanded sanctions authority that Trump has authorized.
The Turkish operation aims to create a corridor of control along Turkey's border that clears out the Syrian Kurdish fighters. Such a "safe zone" would end the Kurds' autonomy in the area and put much of their population under Turkish control. Ankara wants to settle 2 million Syrian refugees, mainly Arabs, in the zone.
Syrian Kurdish authorities said they were evacuating about 4,000 people in the Mabrouka camp, west of Ras al-Ayn, because of artillery fire. Aid groups say there was no direct hit on the camp, located 12 kilometers, or 7 miles, from the border.
Doctors Without Borders said the fighting forced it to shut down a hospital it supports in the border town of Tal Abyad serving more than 200,000 people because most of the residents had to leave, including the medical staff and their relatives.
The group said aid groups had to suspend or limit operations in the al-Hol camp, home to more than 70,000 women and children located 50 kilometers (30 miles) from the Turkish border, as well as the Ain Eissa camp.
El Deeb reported from Beirut. Associated Press writers Suzan Fraser in Ankara, Turkey, and Zeynep Bilginsoy in Istanbul contributed.