BAGHDAD: Two Islamist militant groups in Iraq have rejected a call by al Qaeda to aid Syrian rebels in their revolt against President Bashar al-Assad, saying sending weapons and fighters across the border would only worsen the conflict.

Sunni Islamist al Qaeda leader Ayman al-Zawahri has backed an increasingly violent revolt against Assad, who is from an offshoot of Sh'ite Islam, and is fighting to maintain his grip on 12 years of autocratic rule in mostly Sunni Syria.

The Islamic Army in Iraq, composed of Sunni Arabs and former Iraqi army officers, whose aim was to end U.S. military presence and influence in Iraq, said it would support the Syrians morally in their fight against Assad, but would not dispatch fighters.

"We are against sending fighters, money and weapons to Syria ... we are waiting for the Syrian people to decide their fate but we are supporting their aspirations morally," a senior leader, who declined to be named, told Reuters on Wednesday.

Zawahri, whose group has been struggling to regain its foothold since the killing of former leader Osama bin Laden, has called on Muslims in Turkey, Iraq, Lebanon and Jordan to come to help Syrian rebels confronting Assad's forces.

The Islamic Army leader accused al Qaeda of trying to "steal the revolution" and said if armed fighters were sent, Assad, who blames foreign-backed terrorists for the nearly year-old unrest, would use it as a pretext for his crackdown.

"We do not want to interfere so as not to allow anyone to steal their revolution as al Qaeda has done. We don't want to give the regime a pretext that can be used against the rebels," he said.

Iraq said last week it had reinforced security along its Syrian border to prevent arms smuggling, after reports that weapons and fighters were crossing into Syria, which shares a porous 600 km (370 mile) border with Iraq.

The United States' director of national intelligence said last week al Qaeda in Iraq may have been responsible for bombings in Damascus and Syria's second city, Aleppo.

CREATING SECTARIAN WAR

Iraqi officials and arms dealers have reported an influx of weapons and Sunni Muslim insurgents into Syria from Iraq, but so far it has not seemed to be an organised and sustained flow.

Sheikh Khalid al-Ansari, a senior leader with the Islamist militant al-Rashideen Army, said his group supported the fall of Assad but warned that arming Syria's opposition would create an increasingly sectarian conflict.

"We support the Syrian revolution 100 percent and the fall of the Assad regime," Ansari told Reuters.

"But we do not accept sending weapons, money and fighters to Syria because this will lead to the creation of a sectarian war that will target innocent people similar to what happened in Iraq and we do not want to repeat the same experiment."

Iraq's Shi'ite-led government is worried the unrest in Syria could spill across the border and upset its own fragile sectarian balance.

After the 2003 U.S.-led invasion ousted minority Sunnis from dominance in Shi'ite majority Iraq, the country suffered brutal sectarian warfare in 2006-7 in which tens of thousands of Iraqis were killed.

At the height of the violence, Baghdad blamed Damascus for failing to stem the flow of foreign fighters entering Iraq.

The United Nations says more than 5,000 people have been killed since the uprising against Assad began last March.