Turkish troops and their Syrian Arab allies have captured a cluster of villages around the two towns, which lie in the center of the Kurdish region. The troops have in one place established a front line five miles from the Turkish border, the Turkish vice president, Fuat Oktay, said on Friday evening, according to Turkish media.
Their presence has prompted 100,000 residents to flee south, according to United Nations estimates, and forced the evacuation of a major hospital in Tel Abyad that was run by Doctors Without Borders, an international medical charity.
A second hospital, in Ras al-Ain, was also evacuated, according to a separate report by the Rojava Information Center, an information service run by activists in the region.
Turkish mortar shells also landed close to United States troops near the city of Kobani on Friday, prompting a complaint from the American military, the Turkish Defense Ministry confirmed. No one was killed. Turkish officials said the Americans had not been targeted, though the Pentagon said Turkey had known that United States forces were in the area.
At least 54 Kurdish fighters have been killed since Wednesday, along with 42 from the Turkish-backed force, according to tolls compiled by the Syrian Observatory for Human Rights, a conflict monitor based in Britain.
Turkish towns north of the border have also been affected, as Kurdish fighters have returned fire.
Since fighting began on Wednesday, at least 17 civilians, including four children, have been killed in Turkish border towns. At least four Turkish soldiers have died in the fighting, according to Turkish officials.
An entire Turkish border town — Ceylanpinar — was evacuated, after two girls were killed in a rocket strike Thursday and two people were seriously wounded Friday.