In Talbiseh and across Syria, insurgent fighters who oppose the government of President Bashar al-Assad and the foreign-led militants of the extremist group called the Islamic State are being pummeled by a new wave of attacks and assassination attempts. The assaults are coming at a crucial moment, as President Obama tries to intensify efforts to defeat the Islamic State extremists.

Mr. Obama has ruled out cooperating with Mr. Assad’s military against the extremists, because of the Syrian government’s brutal crackdown on an uprising that started with peaceful protests and grew into civil war. Instead, the United States hopes that insurgent groups it sees as more moderate can, with increased aid, provide the necessary ground forces to fight the extremists in conjunction with American-led airstrikes.

Insurgents of all stripes, except for the Islamic State group, say the Syrian government appears to be stepping up its attacks on them ahead of the threatened American air campaign. Pro-government and antigovernment analysts say Mr. Assad has an interest in eliminating the more moderate rebels, to make sure his forces are the only ones left to benefit on the ground from any weakening of the Islamic State, also known as ISIS.

Mr. Assad has maintained from the start of the conflict that he and his allies are the only force in Syria capable of battling the extremists effectively. But Islamic State activists in Homs said on Wednesday that there had been no recent government airstrikes against the group, adding to opposition suspicions that Mr. Assad prefers to focus on attacking his other opponents while letting the Islamic State’s unchecked brutality argue the case to Syria and the world that his rule is the best alternative.

The Faith in God Brigade in Talbiseh is probably one of the most moderate forces left on the battlefield. Many others have been radicalized by years of inconclusive violence and the influence of foreign fighters and deep-pocketed Islamist donors. For several months recently, parts of the brigade operated under Harakat al-Hazm, an insurgent umbrella group that has received American-made TOW missiles and other aid that the United States has tried to keep out of the hands of more extreme groups.