The remarks by the leader of al-Qaeda's front group in Iraq, Abu Bakr al-Baghdadi, confirmed widespread suspicions of links
between the two groups.
"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 in Iraq and part of it," the SITE monitoring service quoted Baghdadi as saying in an audio speech issued on jihadist forums on Monday.
The groups will now be combined and called the Islamic State in Iraq and the Levant.
Experts have long said that al-Nusra Front was receiving support from al-Qaeda-linked insurgents in neighboring 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.
Baghdadi said the group was willing to ally with other groups "on the condition that the country and its citizens be governed according to the rules dictated by Allah.”
Al-Nusra Front first gained notoriety for its suicide bombings in Syria but has evolved into a formidable fighting force leading attacks on battlefronts throughout the country.
Its suspected affiliation to al-Qaeda's front group in Iraq led to it being labeled a "terrorist” organization by Washington in December.
At the time, the U.S. State Department described it as a "new alias” for al-Qaeda in Iraq, and said it was "an attempt by AQI to hijack the struggles of the Syrian people for its own malign purposes.”
According to the U.S., the head of al-Qaeda in Iraq "is in control of both AQI and Al-Nusra” and reports on Internet forums used by jihadists indicate hundreds of militants have made the trip from Iraq into Syria to fight Assad's regime.
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 Shiite Islam.
The demonstrations were met with bullets, sparking a Sunni backlash and a mostly Islamist armed insurgency increasingly led by the al-Nusra Front.