AKCAKALE, Turkey — Turkish forces pushed deeper into northeastern Syria on Friday, the third day of Ankara’s cross-border offensive against Syrian Kurdish fighters that has set off another mass displacement of civilians and met with widespread criticism from the international community.

There were casualties on both sides and Turkey reported its first military fatality, saying a soldier was “martyred” in the fighting.

Earlier, at least six civilians were reported killed in Turkey and seven civilians have been killed in Syria since Ankara this week launched the air and ground operation into Syria’s northeast. The invasion came after U.S. President Donald Trump opened the way by pulling American troops from their positions near the border and abandoning U.S.-allied Syrian Kurdish fighters.

Trump’s unexpected decision came as he faces an impeachment inquiry at home. It drew swift criticism from Republicans and Democrats in Congress, along with many national defense experts who say it’s endangered not only the Syrian Kurds and regional stability but U.S. credibility as well. The Syrian Kurdish militia was the only U.S. ally in the campaign that brought down the Islamic State group in Syria.

Trump warned Turkey to act with moderation and safeguard civilians. But the barrages of the invasion so far showed little sign of holding back.

In Syria, residents fled with their belongings loaded into cars, pickup trucks and motorcycle rickshaws, while others escaped on foot. The UN refugee agency said tens of thousands were on the move, and aid agencies warned that nearly a half-million people near the border were at risk — in scenes similar to those from a few years ago, when civilians fled the Islamic State group militants.

On Friday morning, plumes of black smoke billowed from the Syrian border town of Tel Abyad as Turkey continued bombarding the area.

The Turkish ministry statement that reported the death of a soldier also said three soldiers were wounded in the action but didn’t provide details. Turkish Defense Minister Hulusi Akar said a total of 342 “terrorists” — Ankara’s parlance for Syrian Kurdish militiamen — were killed in the incursion so far. Those figures could not be independently verified.

Turkey considers the Syrian Kurdish fighters terrorists linked to a Kurdish insurgency within Turkey and says the offensive is necessary for its own national security.

Turkish officials said the Kurdish militia has fired dozens of mortars into Turkish border towns the past two days, including Akcakale, killing at least six civilians, including a 9-month-old boy and three girls under 15. On the Syrian side, seven civilians and eight Kurdish fighters have been killed since the operation began, according to activists in Syria.

The Turkish Defense Ministry said the offensive was progressing “successfully as planned.” Turkey’s official Anadolu news agency said four Turkey-allied Syrian opposition fighters were killed Thursday in a village near the Syrian town of Tal Abyad after an ambush by Syrian Kurdish fighters. The village, Dedat, was later captured by the Turkey-backed rebels, according to the agency.

A Kurdish-led group and Syrian activists said that despite the bombardment, Turkish troops had not made much progress on several fronts they had opened. But their claims could not be independently verified.

On Friday, Russian President Vladimir Putin said he’s worried the Turkish invasion in Syria could unleash the Islamic State group again.

Speaking during a visit to Turkmenistan, Putin said he doubts that the Turkish army has enough resources to promptly take control of the IS prison camps, saying that he fears that the captured IS fighters who have been until now held by the Syrian Kurdish militia “could just run away.”

“We have to be aware of this and mobilize the resources of our intelligence to undercut this emerging tangible threat,” Putin said.

U.S.-allied Syrian Kurdish forces had been holding more than 10,000 IS members captured during the war against the extremists in camps and detention centers in this part of Syria. But this week 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 in its incursion though he acknowledged what he said was Turkey’s legitimate security concern about the Syrian Kurdish fighters.

In a joint news conference with Turkish Foreign Minister Mevlut Cavusoglu, Stoltenberg also expressed worry that the Turkish offensive may “jeopardize” gains made against the Islamic State group in the war in Syria. 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.

As the incursion drew widespread criticism, Turkish President Recep Tayyip Erdogan warned the European Union not to call Ankara’s incursion into Syria an “invasion.” He threatened, as he has in the past, to “open the gates” and let Syrian refugees flood into Europe.

Cavusoglu has said the military intends to move 30 kilometers (19 miles) into northern Syria and that its operation will last until all “terrorists are neutralized.”

Meanwhile, a French official said Friday that sanctions against Turkey will be “on the table” at next week’s European Union summit, over Ankara’s incursion into Syria.

Amélie de Montchalin, the French secretary for European affairs, told France Inter radio that Europe rejected any idea that it was powerless to respond to what she described as a shocking situation against civilians and Europe’s Kurdish allies against the Islamic State group.

European diplomats in Brussels have responded cautiously to the idea of sanctions on Ankara though the invasion — which began Wednesday and was dubbed by Turkey “Operation Peace Spring” — has met with unanimous criticism.

The Turkish assault aims to create a corridor of control along the length of Turkey’s border — a so-called “safe zone” — clearing out the Syrian Kurdish fighters. Such a 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.

The UN refugee agency said tens of thousands of people have fled their homes since Wednesday, while the Britain-based Syrian Observatory for Human Rights, a war monitoring group, put the figure at more than 60,000.

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Associated Press writers Suzan Fraser in Ankara, Turkey, and Zeynep Bilginsoy in Istanbul contributed to this report.