Kurds battle ISIS outside Tal Abayd

Kurdish forces battled Monday to cut a key Islamic State supply line by seizing the border town of Tal Abyad, as terrified Syrians poured into Turkey to escape the fighting.

Forces from the Kurdish People's Protection Units (YPG) backed by Syrian rebels advanced on the southeastern edge of the border town overnight, backed by US-led strikes against ISIS fighters, a monitor said.

The Syrian Observatory for Human Rights said Kurdish forces had seized the Mashur Tahtani area on the southeastern edge of Tal Abyad, with the US-led coalition carrying out at least five strikes overnight.

"The strikes are paving the way for the advance of the Kurdish and rebel forces," Observatory chief Rami Abdel Rahman said.

He said at least 11 ISIS fighters had been killed in clashes and US-led strikes overnight, along with three YPG forces.

Kurdish fighters and Syrian rebels began their advance on Tal Abyad on June 4, and have largely surrounded the ISIS stronghold, prompting thousands of civilians to flee the fighting.

About 16,000 people have fled into Turkey since last week, but the border has closed sporadically.

The flood of refugees has created chaos at times, with some cutting through the border fence or scrambling over loops of barbed wire in frustration at the delay in crossing.

Parents passed screaming children over one section of trampled fencing, and a mother grasped her baby by one arm, a pacifier dangling from its neck.

'Lifeblood channel' for ISIS

Tal Abyad lies some 85 kilometers (50 miles) north of IS's de facto Syrian capital Raqqa, and analysts say it serves as a primary conduit for incoming weapons and fighters, as well as for outgoing black market oil.

"It has been an IS stronghold for a while now, and it has been described as the gateway to Raqqa," said Charlie Winter, a researcher on jihadism at the London-based Quilliam Foundation.

"Certainly, it's of strategic importance because it's a border town through which equipment, recruits, etc can pass."

Tal Abyad is also just 70 kilometers (40 miles) east of the Kurdish-majority town of Kobane, where Kurdish forces battled for months before expelling invading ISIS forces in January.

Tal Abyad "connects the two Kurdish cantons, Jazira and Kobane," in north and northeastern Syria, said Mutlu Civiroglu, a Kurdish affairs analyst.  

"Because of this situation, Kobane was like an island and was vulnerable, so after ISIS was expelled, to prevent any future attack, they (YPG) decided to address the issue of Tal Abyad."

Civiroglu said Tal Abyad serves as the "main lifeblood channel for IS," connecting Raqqa city to the outside world.

"Tal Abyad is a financial and logistical hub for IS. Once you cut this hub it is going to be very hard for IS to smuggle in fighters, to sell oil and deal in the other goods they deal in."

Turkey fears of Kurdish rise

Kurdish forces have been chipping away at ISIS territory in Raqqa province - once completely under the jihadist group's control - for around three months.  

According to the Observatory, they have seized some 50 towns and villages in the province, gradually encircling Tal Abyad from three sides, with only the northern border area still open.

Winter said he expected ISIS to fight hard to keep the strategic town and to mine it heavily.

"I don't think they'll give up without a fight."

The Kurdish advance has prompted criticism from Turkey's President Recep Tayyip Erdogan.  

The Syrian Kurdish forces fighting ISIS are tied to the Kurdistan Workers Party (PKK), which fought a decades-long insurgency in Turkey and is listed as a "terrorist" group by Ankara and its Western allies.  

Nihat Ali Ozcan, an analyst at the Ankara-based TEPAV think tank, said Erdogan's criticism was prompted by fears of rising "separatist sentiment" among Kurds in Turkey's southeast.

"If Tal Abyad is seized by Kurds, after Kobane's liberation, Kurds might emerge as a fighting force against Turkey," Ozcan said.

The Kurdish advance has also prompted allegations of "ethnic cleansing" by some Syrian rebel groups who say YPG forces are expelling Sunni Arabs and Turkmen from the area.  

Kurdish forces reject those allegations, saying they have only asked civilians to evacuate potential battle zones to avoid casualties.