Months after the U.S. initiated military airstrikes in Syria with the stated goal of uprooting Islamic State (or ISIS) militants, new in-depth reporting from the ground in that country reveals that numerous forces once opposed to the group are now citing the U.S.-led bombing campaign as a reason to change their alliances and join the very fighters they once opposed.

According to a series of interviews with the Guardian's Mona Mahmood, members of the Free Syrian Army and other Islamic military groups that were previously engaged in a two-front battle against the Syrian government of President Bashar al-Assad on one side and ISIS on the other, are shifting their thinking, and their military alliances, based on the behavior of the U.S. military.

As Mahmood reports:

Some brigades have transferred their allegiance, while others are forming tactical alliances or truces. Support among civilians also appears to be growing in some areas as a result of resentment over US-led military action.

“Isis now is like a magnet that attracts large numbers of Muslims,” said Abu Talha, who defected from the FSA a few months ago and is now in negotiations with other fighters from groups such as the al-Nusra Front to follow suit.

Assam Murad, a fighter from a 600-strong dissident FSA brigade near Homs said: “There’s no way we would fight Isis after the US military campaign against them.”

A third man, Abu Zeid, the commander of an FSA brigade near Idlib and a defector from President Bashar al-Assad’s army, said: “All the locals here wonder why the US coalition never came to rescue them from Assad’s machine guns, but run to fight Isis when it took a few pieces of land. We were in a robust fight against Isis for confiscating our liberated areas, but now, if we are not in an alliance, we are in a truce with them.”

These and other Syrian fighters told the Guardian in interviews by phone and Skype that the US campaign is turning the attitudes of Syrian opposition groups and fighters in favour of Isis. Omar Waleed, an FSA fighter in Hama, north of Damascus, said: “I’m really scared that eventually most of the people will join Isis out of their disappointment with the US administration. Just have a look on social media websites, and you can see lots of people and leaders are turning to the side of Isis."

Some of those interviewed by Mahmood echoed critics of the U.S. strategy to bomb Syria by saying that the "it was inevitable" that U.S. airstrikes would in many ways bolster, not undermine, support for ISIS.