Hezbollah chief Hassan Nasrallah warned Al-Qaeda on Sunday that it had been tricked into fighting in Syria, and that the rebellion would not be able to topple the regime of President Bashar al-Assad militarily.

"The Americans, Europeans and some governments in the Arab and Muslim world have set a trap for you in Syria," the head of Lebanon's most powerful military force said.

"They have opened the entire country for you to congregate there from all corners of the world and kill one another," he said, in a speech broadcast during an annual university graduation ceremony in the southern suburbs of Beirut.

"And you are complicit in this trick," Nasrallah added.

His comments came amid increased debate over the rise of jihadist groups in Syria, notably the Al-Nusra Front, which was blacklisted as a terrorist organisation by Washington last week for its alleged links to Al-Qaeda in Iraq.

"If we assume that these groups which are affiliated to Al-Qaeda and its ideology are able to achieve a breakthrough on the ground one day, then they will be the first to pay the price in Syria as they have in other countries," he said.

The Hezbollah leader, whose group is a longstanding Assad ally, said that the situation in Syria "is becoming increasingly complex".

"The opposition believes they will be able to resolve the battle militarily, which is very, very, very suspect."

Nasrallah said the conflict pitched a regime "defending its existence out of conviction with the majority of the Syrian people behind it" against an "armed opposition working to topple the regime with a segment of the population in support".

He said he feared the conflict would be a protracted one, "as long as the armed opposition and its regional and international backers refuse any dialogue with the regime."

Damascus and its allies accuse Qatar and Saudi Arabia of funnelling arms to the rebels through neighbouring Turkey with Western connivance. The opposition rejects any dialogue until Assad quits.

The Americans want to prolong the Syrian crisis "because more death among the armed opposition, the Syrian army and security services, and the people will render Syria weak, impoverished, devastated and drained," Nasrallah said.

"It will be crossed off the regional power balance ... for the benefit of America and Israel," he added.