"The Al-Nusra Front is simply a branch of the Islamic State of Iraq," the head of the Al-Qaeda in Iraq front group, Abu Bakr al-Baghdadi, said Tuesday in a recording posted online.

Describing Al-Nusra leader Abu Mohammed al-Jawlani as "one of our soldiers," he said the two groups would merge under the banner of their State in Iraq and the Levant.

Baghdadi's comments came a day after an Al-Nusra-style suicide bombing in the heart of Damascus killed at least 15 people and wounded 146.

They also came after Al-Qaeda's global chief, Ayman al-Zawahiri, urged all militants to fight to establish a new state in Syria, in an audio message posted on the Internet on Sunday.

Al-Nusra, which announced its creation in a January 2012 video, is a magnet for foreign militants seeking to take part in the insurgency against Assad's government.

Since beginning of the unrest in March 2011, the Syrian government has insisted that the insurgency, that has left thousands of people dead, was orchestrated from outside the country.

The New York Times reported last month that the CIA was helping Arab states and Turkey to boost arms shipments to Syria's rebels.