The Iraqi wing of al-Qaeda announced that a rebel group at the forefront of the rebellion in Syria was its branch in that country and that both groups would operate under one name, according to the US-based SITE Intelligence Group.
The leader of the Islamic State in Iraq, Abu Bakr al-Baghdadi, said his group and Syria's al-Nusra Front - which has been blacklisted by the United States - would now jointly go under the name of the Islamic State in Iraq and the Levant, the SITE Intelligence Group reported.
The predominant Islamist element in the Syrian uprising has created concern for regional and Western powers and deepened the Shi'ite-Sunni divide in the Middle East.
The authenticity of the statement could not immediately be verified.
If confirmed it is likely to further deepen the political dilemma facing those countries who oppose Syrian President Bashar al-Assad but fear the rise of al Qaeda and Islamist militancy in Syria.
"It's now time to declare in front of the people of the Levant and (the) world that the al-Nusra Front is but an extension of the Islamic State of Iraq and part of it," the SITE monitoring service quoted Baghdadi as saying in an audio speech issued on jihadist forums on Monday.
Experts have long said that al-Nusra Front was receiving support from al Qaeda-linked insurgents in neighbouring Iraq.
The group has claimed responsibility for deadly bombings in Damascus and Aleppo, and its fighters have joined other rebel brigades in attacks on Assad's forces.
At least 70,000 people have been killed since protests led by Syria's Sunni Muslim majority broke out two years ago against Assad, who belongs to the minority Alawite sect, an offshoot of Shi'ite Islam.
The demonstrations were met with bullets, sparking a Sunni backlash and a mostly Islamist armed insurgency increasingly led by the al-Nusra Front.
The US State Department in December designated the group a foreign terrorist organisation.