BEIRUT -- U.S.-backed Kurdish fighters captured large sections of a strategic town on the Syria-Turkish border on Monday, dealing the biggest setback yet to the Islamic State group, which lost a key supply line for their nearby self-proclaimed capital.
The seizure of Tal Abyad threatened to flare tensions between Kurds and ethnic Arabs, who accused the Kurdish militia of deliberately displacing thousands of people from the town, which has a mixed population.
Redur Khalil, a spokesman for the main Kurdish fighting force, known as the YPG, said Kurdish fighters entered from the east and were advancing west toward the town's centre amid fierce clashes with pockets of IS resistance.
"We expect to have full control over Tal Abyad within a few hours," he told The Associated Press by telephone. A few hours later, the YPG announced on its Facebook page that it had liberated the town.
The Britain-based Syrian Observatory for Human Rights confirmed the Kurdish fighters had "almost full control" of Tal Abyad by Monday evening, and had taken command of the border crossing with Turkey. It said some 40 Islamic State militants were targeted by U.S.-led airstrikes as they tried to flee south.
An AP photographer in Akcakale, on the Turkish side of the border, saw several dozen YPG fighters waving their yellow triangular flag and flashing victory signs. Earlier, several dozen Kurdish gunmen were seen running up a hill, moving west.
A few people on the Syrian side of the border were seen raising the green, white and red flag of the Free Syrian Army before being apprehended by Turkish security after they broke a hole in the border fence. A contingent of Free Syrian Army fighters is battling alongside the Kurds in an effective alliance against the Islamic State group called "Burkan al-Furat," or Volcano of the Euphrates.
The loss of Tal Abyad, some 80 kilometres north of Raqqa, the capital of the Islamic State group's self-declared caliphate, is the extremists' biggest setback since Kurdish fighters took control of the Kurdish border town of Kobani near Turkey, after fighting IS for months.
A Kurdish victory in Tal Abyad deprives the militant group of a direct route for bringing in foreign militants and supplies, and links the Kurds' two fronts, putting even more pressure on Raqqa.
An anti-IS media collective based in Raqqa said the extremists set up checkpoints in the centre of the city on Monday and installed security cameras in a main square.
Earlier, Kurdish units marching west from Kobani and others marching east from the Kurdish town of Ras al-Ayn met up in the village of Qaysariyeh, some three kilometres south of Tal Abyad as they encircled the town from three sides, leaving Turkey as the only outlet.
As with the Kurdish victory in Kobani, the YPG fighters' advance under the cover of the U.S-led air campaign highlighted the decisive importance of combining airstrikes with the presence of a cohesive and motivated ally on the ground -- so clearly absent in Iraq and other parts of Syria.
With most of Syria now controlled by either Islamic State militants or forces loyal to President Bashar Assad, the U.S. has found a reliable partner in the YPG, a group of moderate, mostly secular Kurdish militiamen driven by revolutionary fervour and the desire for self-rule.
Since the beginning of the year, they have wrested back more than 500 mostly Kurdish and Christian towns in northeastern Syria, as well as strategic mountains seized earlier by the Islamic State group. They have recently pushed into Raqqa province, an IS stronghold where Tal Abyad is located.
The Kurdish advance has caused the displacement of more than 16,000 people who fled to Turkey in the past two weeks. On Monday, up to 3,000 more refugees arrived at the Akcakale border crossing, according to Turkish state-run TRT television. An AP photographer saw large numbers of people at the border and thick smoke billowing as U.S.-led coalition aircraft targeted IS militants in Tal Abyad.
As Kurdish fighters push deeper into Islamic State strongholds in northern Syria, tensions with ethnic Arabs and Turkmen in the region have risen.
On Monday, more than a dozen Syrian rebel groups accused the Kurdish fighters of deliberately displacing thousands of Arabs and Turkmen from Tal Abyad and the western countryside of predominantly Kurdish Hassakeh province. In a statement, they accused the YPG of committing "ethnic cleansing" -- a charge strongly denied by the Kurds.
The accusation, which was not backed by evidence of ethnic or sectarian killings, threatened to escalate tensions between ethnic Arabs and Kurds as the Kurdish fighters conquer more territory in northern Syria.
"YPG forces ... have implemented a new sectarian and ethnic cleansing campaign against Sunni Arabs and Turkmen under the cover of coalition airstrikes which have contributed bombardment, terrorizing civilians and forcing them to flee their villages," the statement issued by rebel and militant groups said.
The 15 rebel groups, including the powerful ultraconservative Ahrar al-Sham and Jaish al-Islam, said the alleged ethnic cleansing was concentrated in Hassakeh province and in Tal Abyad, and was part of a plan by the Kurdish Democratic Party, or PYD, to partition Syria. The YPG, or People's Protection Units, is the armed wing of the PYD. The movement is affiliated with the Kurdish PKK, which has waged a long and bloody insurgency in southeastern Turkey.
The statement echoed comments last week by Turkish President Recep Tayyip Erdogan.
"On our border, in Tal Abyad, the West, which is conducting aerial bombings against Arabs and Turkmen, is unfortunately positioning terrorist members of the PYD and PKK in their place," Erdogan said.
Khalil, the YPG spokesman, strongly refuted the claim, and seeking to calm nerves, said the YPG is a Syrian national group whose battles are directed solely against the Islamic State group.
"We say to residents of Tal Abyad, there is no reason for you to cross to another country (Turkey). Our towns are open to you, you are our people and you will return to your towns, villages and properties," he said.
He pledged that the YPG will not interfere in administering Tal Abyad once it falls, leaving it to civilian committees.
