Turkey pressed its assault against U.S.-allied Kurdish forces in northern Syria on Thursday for a second day. Turkey pounded the region with airstrikes and an artillery bombardment that raised columns of black smoke in a border town and sent panicked civilians scrambling to get out.

Residents fled with their belongings loaded into cars, pickup trucks and motorcycle rickshaws, while others escaped on foot. The U.N. 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.

People run to take cover after mortars fired from Syria, in Akcakale, Turkey, Thursday, Oct. 10, 2019. An Associated Press journalist said at least two government buildings were hit by the mortars in Sanliurfa province's border town of Akcakale and at least two people were wounded. Ismail Coskun / AP

It was a wrenchingly familiar scene for many who had fled ISIS militants only a few years ago.

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The Turkish air and ground assault was launched three days after President Trump opened the way by pulling American troops from their positions near the border alongside their Kurdish allies. Mr. Trump dismissed concerns that Turkey's incursion into northern Syria could enable hundreds of hardened ISIS fighters to go free as a problem for other countries.

At a time when Mr. Trump faces an impeachment inquiry, the move drew swift criticism from Republicans and Democrats in Congress, along with many national defense experts, who say it has endangered not only the 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 ISIS in Syria.

People help a wounded boy as they take cover after mortars fired from Syria, in Akcakale, Turkey, Thursday, Oct. 10, 2019. Ismail Coskun / AP

Commanders of the Kurdish-led Syrian Democratic Forces (SDF) told CBS News they've had to put their operations against ISIS on hold to confront the Turkish invasion, and a senior U.S. military official confirmed to CBS News that operations against ISIS were "effectively paused."

The SDF said the Turkish offensive was jeopardizing security at the overcrowded prisons housing the thousands of ISIS inmates, risking breakouts and a possible ISIS resurgence.

Mr. Trump warned Turkey to act with moderation during its assault and safeguard civilians. But the opening barrage showed little sign of holding back: The Turkish Defense Military said its jets and artillery had struck 181 targets so far.

More than a dozen columns of thick smoke rose in and around the town of Tel Abyad, one of the offensive's first main targets. Turkish officials said the Kurdish militia has fired dozens of mortars into Turkish border towns the past two days, including Akcakale.

Turkish officials in two border provinces said mortar fire from Syria killed 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.

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.

Turkish President Recep Tayyip Erdogan said 109 "terrorists" were killed in the offensive, a reference to the Syrian Kurdish fighters. He did not elaborate, and reports from the area did not indicate anything remotely close to such a large number of casualties.

Erdogan also 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.

Turkish Foreign Minister Mevlut Cavusoglu said the military intends to move 19 miles into northern Syria and that its operation will last until all "terrorists are neutralized."

The Syrian Kurdish fighters, along with U.S. troops, have been involved in mopping-up operations against ISIS fighters still holed up in the desert after their territorial hold was toppled earlier this year.

Turkey considers members of the Kurdish militia to be "terrorists" because of their links to the outlawed Kurdistan Workers' Party, or PKK, which has led an insurgency against Turkey for 35 years. The conflict has killed tens of thousands of people. The U.S. and other Western countries also consider the PKK a terrorist group.

Turkey, a NATO member, considers its operations against the Kurdish militia in Syria a matter of its own survival, and it also insists it won't tolerate the virtual self-rule that the Kurds succeeded in carving out in northern Syria along the border.

The Turkish assault aims to carve out a corridor of control along the length of the border — a so-called "safe zone" — clearing out the Kurdish militia. Such a zone would end the Kurds' autonomy in the area and put much of their population under Turkish control. Ankara has said it aims to settle 2 million Syrian refugees, who are mainly Arabs, in the zone.

Turkey began its offensive in northern Syria on Wednesday with airstrikes and artillery shelling, and then ground troops crossed the border later in the day. CBS News correspondent Charlie D'Agata reported the first day of the offensive was more intense than expected. They unleashed an onslaught of artillery and airstrikes targeting the Syrian towns of Tal Abyad and Ras al-Ain, and the Turkish government confirmed Thursday that a ground offensive was also underway.

Mustafa Bali, a spokesman for the Kurdish-led Syrian Democratic Forces, said their fighters have repelled Turkish forces ground attacks.

"No advance as of now," he tweeted Thursday.

But Maj. Youssef Hammoud, a spokesman for Turkish-backed opposition fighters participating in the operation, said they captured the village of Yabisa, near Tal Abyad, a spokesman for the fighters said. In a tweet, he called it "the first village to win freedom."

Turkey's state-run news agency said the allied Syrian fighters had cleared and entered a second village, Tel Fander, but provided no details. The Britain-based Syrian Observatory for Human Rights said Turkish commandos entered the village of Beir Asheq.

The Observatory said more than 60,000 people have fled their homes since Wednesday, while the UNHCR estimated it at tens of thousands. It called on parties to adhere to International Humanitarian Law, including providing access for aid agencies.

International aid agencies warned of an escalating humanitarian crisis, saying that civilians were at risk "as violence escalates."

The statement was co-signed by 14 organizations, including Doctors of the World and Oxfam, saying an estimated 450,000 people live within 5 kilometers (3 miles) of the border with Turkey "and are at risk if all sides do not exercise maximum restraint and prioritize the protection of civilians."

There already are more than 90,000 internally displaced people in the region, it said, with camps and detention centers holding tens of thousands of fighters with families.