Rebel Islamist 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 al-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 21 / 2-year-old 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.

As of Sept. 4, lawmakers appear to be tentatively dividing into four camps over military action in Syria.

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-Qaeda-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 living in rebel-held territory.

The Syrian Islamic Front, led by Ahrar al-Sham and including a number of smaller Salafist groups, describes itself as Islamist but is considered less extreme than the radical groups designated as terrorist organizations by the United States that have served as magnets for foreign fighters across the region.

Ahrar al-Sham has established a presence across wide swathes of Syrian territory, notably in the north, and probably has broader support among ordinary Syrians than the extremists.

For such groups, the prospect of American intervention after more than two years of repudiation represents something of a dilemma, analysts say. Islamist groups have thrived on the rejection by the West of appeals by more moderate Syrian opposition figures for help.

But at the same time, groups such as Ahrar al-Sham could benefit militarily should the attacks take place, said Charles Lister of the London-based defense consultancy IHS Janes.

“The reality is that for most of the non-al-Qaeda hardline Islamist groups, it could turn out to be in their interests for these strikes to take place,” he said. “But they can’t be seen publicly to defend them because of Western involvement. That’s why we’re seeing such pragmatic and ambivalent statements.”

It is also not in the Islamists’ interests to alienate the many ordinary Syrians living in rebel-held areas who say they are eager for any intervention that might accelerate the war’s end. Activists in the northern province of Idlib issued a video Friday directly addressing members of Congress, interspersing footage of dead children with appeals from children, in English, for intervention.

A spokesman for Ahrar al-Sham, contacted in Idlib, stressed that the Syrian Islamic Front statement was intended neither to support nor oppose American intervention, only to advise Syrians of the implications.

The warnings came as the U.S. Embassy in Beirut announced that all nonessential personnel and the families of diplomats had been withdrawn from Lebanon, amid growing tensions across the region in anticipation of American military action.

A statement issued by the Embassy said those affected had departed Friday, and it urged Americans not to travel to Lebanon. It also called on those already in the country to “carefully consider” the dangers of remaining in Lebanon, which is considered at risk for retaliatory attacks against U.S. interests if the Obama administration goes ahead with the threatened strikes.

The State Department also urged Americans to defer nonessential travel to southern Turkey. The U.S. consulate in the Turkish city of Adana, near the U.S. military base at Incirlik, has been authorized to draw down non-emergency staff and family members “because of threats against U.S. government facilities and personnel,” a separate statement said.

Karen DeYoung contributed to this report from Washington.