In Syria's Aleppo, devastated by two years of fighting and regime attacks, rebels and activists are eager for US strikes against jihadists they say have stolen their anti-government uprising.

The United States has yet to decide on whether it will carry out air strikes in Syria against jihadists from the Islamic State group, though it is already doing so in neighbouring Iraq.

The Islamic State's campaign of extreme violence and abuses against both civilians and rival opposition groups has prompted a backlash across rebel-held Syria, where many hope the US air campaign next door will be extended.

"We support US strikes against Daesh," said Abu Al-Muqdad, a fighter in Aleppo with the Islamic Front, a rebel coalition, using the Arabic acronym for the Islamic State (IS).

"They have ravaged the country, oppressed the people, make no distinction between combatants and civilians and slaughtered with knives," he said.

Calls for US action in Syria have been mounting in the wake of IS advances in Iraq and Syria, as well as the brutal killing of US journalist James Foley, who was held hostage.

US military officials have acknowledged the group cannot be defeated just with its air strikes in Iraq, which began on August 8 after lightning advances by IS militants.

"I hope they bomb them and not a single one is left. Those people are not Muslims, they are infidels," added another rebel officer, who heads a special operations battalion within the Islamic Front coalition.

- Rebels fought IS -

Syrian rebels initially welcomed jihadist fighters into their battle against Syrian President Bashar al-Assad.

But IS's insistence on dominating territory captured from the regime, its harsh interpretation of Islam and abuses including decapitations have alienated many rebels and civilians.

In January, rebel groups began fighting against IS in territory under opposition control and managed to expel it from much of northern Syria.

But it has since regrouped, seizing territory and weapons in Iraq and taking both lost ground and new territory in Syria, including in northern Raqa, where it now controls the entire province.

The advances prompted the Syrian regime to reverse a long-standing policy of largely ignoring IS bases in their air raids on rebel territory and begin a series of strikes against the group's strongholds.

But many rebels continue to see IS and the Syrian regime as two faces of the same coin.

"I'm in favour of American air strikes on the areas controlled by Daesh because they and the regime, they're one and the same," said Jaber, who heads the Islamic Front's military police unit in eastern Aleppo city.

"The regime is bombing us with explosive barrel bombs and Daesh is killing our people with knives," he said.

Aleppo province has been subject to a particularly fierce regime aerial campaign, including the use of explosive-packed barrel bombs tossed from regime helicopters that rights groups say kill indiscriminately.

- IS 'a new enemy' -

Activist Abdullah is equally eager to see IS militants targeted.

"Daesh is a new enemy that hides under the cover of Islam. It's totally unacceptable."

But while many rebels would be happy to see the US intervene against IS, they also express suspicion that American action would come after Damascus urged international cooperation against jihadists.

Earlier this week, Syria's Foreign Minister Walid Muallem said the government was willing to cooperate with any country, including the United States, against "terrorists".

But the Syrian government deems all those seeking to oust Assad to be "terrorists," and rebels are not keen to see Washington ally with the regime they have been fighting since March 2011.

"What the foreign minister says implies that a possible US strike would be in the interests of the regime. I'm against it," said Mohammed, an activist in Aleppo.

Others in the city, which has been divided between rebel control in the east and regime control in the west since shortly after fighting began there in mid-2012, question US willingness to act in Syria now.

"We have suffered for three years and all the calls for strikes against the regime have not been heard," said Bou Yussef, a nurse in Aleppo.

"Every day I receive dozens of women, men and children mutilated by explosive barrel bombs. What we need is strikes against the regime," he said.