Has the US picked a favorite ally in its fight against ISIS?

After two days of intensified, US-led coalition air strikes in northern Syria, Syrian Kurdish fighters have recaptured more than 10 villages held by the Islamic State near Raqqa, the Syrian Observatory for Human Rights reported. At least 78 Islamic State militants have been killed in on-the-ground combat since Sunday, the Observatory said. 

This weekend’s aerial attacks have been one of the most sustained since the US began its offensive against the militant group last September.

With the aid of smaller Syrian rebel groups, the People’s Protections Units (YPG) have defeated Islamic State in several attacks in recent weeks. Yet the terrorist group is still in control of Ain Issa, a town north of Raqqa, after it was captured from the YPG on Monday, the Observatory said.

Since the YPG nearly expelled the Islamic State from the Syrian town of Kobane in January, the Kurdish militia has proved itself to be an important ally for the US-led alliance in its attempts to overthrow Islamic State groups in Syria and Iraq.

On Monday, Barack Obama emphasized the Kurds’ significant role in combatting the militant group, stressing that US forces have limited capabilities. “It must be the job of local forces, with training and air support” from the US-led coalition, he said. 

While the YPG has maintained a strong presence in the predominantly Kurdish areas in northern Syria, the coalition hasn’t been able to cooperate with enough rebel fighters in the remaining territories controlled by the Islamic State. The terrorist group is now “dug into the civilian population,” Obama said, complicating further the US’s recruitment and military training program.

Since Obama signed legislation that would allow the US to arm and train rebel forces in Syria and Iraq last September, the US has sent more than 3,000 troops to advise and aid the fraught Iraqi military, according to The Associated Press. Yet the coalition has been struggling to train and equip local forces in both Iraq and Syria.

In February, Nick Heras, research associate in the Middle East Security Program at the Center for a New American Security, told The Christian Science Monitor that the US training mission is “not going to work overnight – or even over the course of the year.” His predictions were right.

Last month, Obama said that the US lacks a "complete strategy" for training Iraqi troops. In addition, American troops only started training a small group of 90 Syrian fighters in May, far less than the goal of recruiting 5,400 fighters a year. 

The coalition’s screening process, though vital, has also delayed and limited training and recruitment efforts. According to a Congressional Research Service report from September, the coalition will have a difficult time identifying moderate opposition forces who haven’t cooperated with extremists in the past, and whose aims coincide with that of the coalition.

“Some opposition forces seek to cast themselves as potential allies to outsiders who are opposed to both the Islamic State and the Syrian government,” it says, “while others reject the idea of foreign intervention outright or demand that foreigners focus solely on toppling President Asad.”

According to Mr. Heras, the research associate, recruitment “must be built on trust​: ​on the Syrian opposition side that the US will support it, and on the US side that these groups are in it for long haul – and are not opportunists.”