Thousands of Syrian Kurds and Arabs pushed through the Turkish border Friday as they fled the Islamic State’s latest advance in Syria. By sundown, the militants had taken more than 60 villages in northern Syria, according to observers.

The Syrian Observatory for Human Rights, a group based in Britain, says tens of thousands of residents have fled their homes ahead of the Islamic State surge, adding to the over 3 million Syrians who have already sought refuge in neighboring countries. Turkey, which already hosts more than 800,000 Syrian refugees, at first kept the border closed Friday, before finally allow the flood of new refugees to enter.

The Islamic State’s rapid advance prompted calls for international military support, and specifically from the United States, for the Syrian Kurdish fighters.

“We are in desperate need of the American strikes,” said Redur Xelil, the spokesperson of the People’s Protection Units (YPG), one of the Kurdish groups fighting the Islamists. “There is now an international alliance under American command to fight ISIS. I think it is time to hit them.”

The YPG forces have been battling the Islamic State troops for more than three days in these villages. Xelil said his fighter’s weapons are no match for the looted American arms the militants took from fleeing Iraqi soldiers in June.

“ISIS has highly advanced and sophisticated American weapons. We need weapons too,” said Xelil. “ISIS is now aiming to take over Kobane as they aimed to take over Erbil.”

The first U.S. airstrikes against Islamic State forces were in support of the Iraqi Kurdish peshmerga forces in August as Islamic State forces approached Erbil, the de-facto capital of the Kurdistan Regional Government (KRG) in northern Iraq. For Washington, that was a relatively easy move — the Iraqi Kurds are longtime allies: Kurdish peshmerga fighters fought alongside U.S. Army troops against Saddam Hussein’s forces during the Iraq war.

“I’d like to ask the international community to take every measure as soon as possible to save Kobane and the people of west Kurdistan from the hands of the terrorists,” said KRG President Massoud Barzani in a statement Friday. “The ISIS terrorists . . . have to be hit and defeated wherever they are.”

It was the U.S. airstrikes, along with shipments of small arms and military advisers, that has allowed Iraqi Kurds and Iraqi national forces to slow the Islamic State’s march through Iraq, and for them to retake some villages and key infrastructure, such as the Mosul Dam.

But supporting the Syrian Kurds is a more complex issue.

“Part of ISIS’s M.O. is to go after low-hanging fruit,” said Kenneth M. Pollack, a specialist in Middle East political military affairs and a former CIA analyst. “One of the signs of how sophisticated they are is that they are constantly looking for weak spots.”

Despite being capable fighters, the Syrian Kurdish YPG forces are one of these weak spots because they lack a strong alliance with either the moderate Syrian rebels or the Assad regime. Many of the rebel groups trying to overthrow Syrian President Bashar al-Assad view the Syrian Kurds with suspicion, considering them agents of the regime. Some Syrian rebel groups aligned with the Islamic State last year and actually fought against YPG forces.

“Overthrowing Assad’s regime is not exactly a priority of the YPG,” said Aymenn al-Tamimi, an expert on Syrian and Iraqi militants from the Philadelphia-based Middle East Forum. In fact, while Kurdish forces have clashed with Syrian government troops on occasion, they have also quietly co-existed in some areas. “In the end the Kurds want to maintain control over their areas and keep out intruders.”

Al-Tamimi says the relationship between Kurdish forces and other rebel groups has thawed this year as both began to see the Islamic State as a key enemy. In some locations, the forces are now coordinating on a local level. Xelil said in the current battles, the YPG is coordinating with the Free Syrian Army through a joint operations room. He said more Kurdish fighters arrived from Turkey on Friday, answering calls from Kurdish leaders to stand with their brethren.

While U.S. Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said Thursday that the United States was considering sending arms to the Syrian Kurds, even if they coordinate with the FSA, U.S. support to these groups will be complicated.

What raises concern for many is how long the Kurds plan to keep the control they earn in these areas. While Assad has been busy, the Kurds have solidified their rule over parts of Syria they see as Kurdish. While many states seems to be getting comfortable with the idea of a independent Iraqi Kurdistan, the idea of pushing that border into Syria, or carving out a separate autonomous Syrian Kurdish region, will spur reaction from states like Turkey that the U.S. needs as allies for the fight against the Islamic State.

“If it looked like we were supporting a pan-Kurdish state they would get very unhappy. That is not something that the Turks want,” said Pollack. Turkey has fought a Kurdish insurgency in its own borders and may be uncomfortable with spreading Kurdish independence, along with Iran and even Baghdad. “So supporting the Syrian Kurds is actually really politically problematic for the United States.”

But the pressure may mount on Washington to intervene as leaders warn of a massacre if the Islamic State pushes further in to these areas.