QALAT AL MUDIQ, Syria -- When the group Jabhat al Nusra first claimed responsibility for car and suicide bombings in Damascus that killed dozens last January, many of Syria’s revolutionaries claimed that the organization was a creation of the Syrian government, designed to discredit those who opposed the regime of President Bashar Assad and to hide the regime’s own brutal tactics.

Nearly a year later, however, Jabhat al Nusra, which U.S. officials believe has links to al Qaida, has become essential to the frontline operations of the rebels fighting to topple Assad.

Not only does the group still conduct suicide bombings that have killed hundreds, but they’ve proved to be critical to the rebels’ military advance. In battle after battle across the country, Nusra and similar groups do the heaviest frontline fighting. Groups who call themselves the Free Syrian Army and report to military councils led by defected Syrian army officers move into the captured territory afterward.

The prominence of Nusra in the rebel cause worries U.S. and other Western officials, who say its operations rely on the same people and tactics that fueled al Qaida in Iraq – an assertion that is borne out by interviews with Nusra members in Syria.

Among Nusra fighters are many Syrians who say they fought with al Qaida in Iraq, which waged a bloody and violent campaign against the U.S. presence in that country and is still blamed for suicide and car bombings that have killed hundreds of Iraqis since the U.S. troops left a year ago.

According to Nusra members, some of the group’s leaders, including the emir, or top ruler, in Syria’s Deir al Zour province, are Iraqis.

The group’s prominence makes clear the dilemma of Syria’s revolutionaries, as well as those who might provide support to them. Though members of Nusra operate independently of the other rebel groups that have taken up arms _ and particularly those that are calling for elections if Assad is deposed _ it is increasingly clear that their operations are closely coordinated with more secular rebels.

Some Syrians say that Nusra’s importance is a result of the West’s failure to support those secular rebels. But the closeness of the coordination between Nusra and other rebels makes it difficult to support one without empowering the other.

Nusra leaders argue that the West should not fear their rise in importance.

“The West must not fear Islam _ when Islam is in power, all people will live peacefully,” said Iyad al Sheikh Mahmoud, the leader of a recently founded Jabhat al Nusra group in this central Syrian city of about 30,000. Before becoming the leader of Nusra’s group here, Mahmoud had been part of Ahrar al Sham, another group of fighters that has branches across the country and subscribes to a similar ideology.

“There is no difference at all between the ideology of Ahrar al Sham and Jabhat al Nusra,” Mahmoud said, indicating that he had largely changed groups for the opportunity to lead one. Like Nusra, Ahrar al Sham is also not aligned with the military councils.

Nusra’s rise is most evident in Syria’s north and east, where anti-Assad forces have recently been racking up impressive military gains. Gone are the days just five months ago when Nusra’s actions seemed limited to car and suicide bombings. Now, Nusra fighters are organized in battalion-sized groups that are often armed with heavy weaponry.