BEIRUT – Islamist rebel groups are expressing opposition to U.S. strikes against the Syrian regime, putting them at odds with the leadership of the mainstream Free Syrian Army and underscoring the deep rifts within Syria’s opposition that threaten to complicate future efforts to end to the war.

The leading hard-line Islamist group in northern Syria issued a statement on its Facebook page cautioning its followers against supporting U.S. intervention, saying it would only serve American interests and not the cause of those seeking to topple President Bashar Assad.

The Syrian Islamic Front, which is dominated by the Salafist Ahrar al-Sham group, stopped short of directly opposing American intervention in Syria’s conflict, which many in the opposition hope would accelerate the fall of Assad’s regime. But, the group warned on its Facebook page, the true goal of U.S. attacks would be to “advance the interests of the perpetrators.”

Another gathering of smaller Islamist groups issued a video condemning outright the threatened strikes, which the Obama administration has said are needed to deter further use of chemical weapons after hundreds of people were killed in the suburbs of Damascus in a poison gas attack widely blamed on government forces.

“We reject Western military intervention in Syria and consider it a new aggression against Muslims,” said a group of fighters who identified themselves as representatives of eight “jihadi brigades,” according to a video posted on YouTube.

The statements underscored the complexity of the rebel landscape across Syria, where hundreds of small rebel units have sprung up, banded together, split and formed new alliances over the past two years. The Supreme Military Council, which claims to represent the majority of moderate Free Syrian Army units and has long appealed for Western support, has embraced the Obama administration’s proposal for strikes.

At the opposite end of the spectrum, extremist jihadi groups have expressed fears that they are the real targets of the American threats. The al-Qaida-affiliated Islamic State of Iraq and the Levant and Jabhat al-Nusra have been vacating their headquarters and relocating their assets ahead of any possible strikes in case they are also hit, according to Syrians in rebel-held territory.

Meanwhile, Secretary of State John F. Kerry and French Foreign Minister Laurent Fabius sought to rebut the notion Saturday that their nations are alone in backing a military strike against Syria even after France joined its European counterparts in seeking a delay.

“There’s a growing consensus to take action,” Fabius said at a press conference with Kerry in Paris. “The U.S. and France are not isolated.”

The allies commented hours after France and other European Union members said in a statement after a foreign ministers’ meeting in Vilnius, Lithuania, that action should await a United Nations report on Syria’s alleged use of chemical weapons.