Al Qaeda in Iraq admits it is fighting in Syria
The statement was made in a 21-minute audio message posted in jihadist forums on Monday, according to news agencies and the US-based SITE intelligence Group.
Postings on other websites used by militants appeared to confirm the link - although there was no immediate statement of affirmation from Jabhat Al Nusra yesterday.
"It's now time to declare in front of the people of the Levant and the world that the Nusra Front is but an extension of the Islamic State of Iraq and part of it," SITE quoted Abu Bakr Al Baghdadi, head of the Islamic State of Iraq, as saying.
Mohammed Al Jolani, described in the audio statement as one of Al Qaeda in Iraq's "soldiers" will lead the Syrian arm, he said.
Jabhat Al Nusra is a secretive organisation, that has portrayed itself home grown in Syria rather than driven by foreign jihadis, although activists and analysts in Syria say foreign fighters are heavily involved. It has largely sought to keep clear of the Al Qaeda or Islamic State of Iraq label.
In December the Untied States classified Jabhat Al Nusra, which means The Support Front for the Syrian People, as a terrorist organisation, on the grounds it was an affiliate of Al Qaeda in Iraq.
Iraqi security forces have made a similar link, saying Islamic militants who had fought US and Iraqi government troops following the US-led invasion of 2003, had moved to Syria with the start of the uprising there in March 2011.
This apparent acknowledgement of these close links will not, therefore, come as a surprise to western intelligence agencies.
It is, however, likely to pose a serious political challenge to the Syrian National Coalition, the opposition group recognised and supported by western and Arab states.
Moaz Al Khatib, the National Coalition's president, rejected the US's terrorist classification when it was made and, tacitly endorsing Al Nusra, urged Washington to reconsider.
Any group fighting for the overthrow of Bashar Al Assad should be left to do so, he said.
Al Nusra Front has emerged as one of the most powerful forces fighting the Syrian regime, its discipline and effectiveness often standing in stark contrast to the ramshackle and ill-equipped Free Syrian Army (FSA) factions.
It has been behind important rebel gains, including the seizure of military bases and Raqqa city, the first provincial capital to fall to the opposition.
Crucially, Al Nusra has also won the admiration of some Syrians living in areas under its control, for its humanitarian aid efforts and its crackdown on looting. At the height of its power in Iraq, Al Qaeda alienated the local population with its brutality, intolerance and sectarianism, provoking a deadly backlash by Iraqi tribes.
While Nusra fighters are not part of the FSA - the National Coalition's armed wing - they have frequently worked together on the ground inside Syria, coordinating efforts against regime military units.
There are however, differences in various groups' ultimate aspirations. Even home-grown rebel factions say they want Muslim law established within Syria, eschewing extra territorial ambitions, while Al Qaeda and its affiliates seek to establish an Islamic caliphate across the entire middle east.
By yesterday afternoon there had been no official reaction from the National Coalition.
With a rebel assault on Damascus rumoured to be under preparation, it would be a serious setback for Syria's moderate opposition, and their international backers, if the capital were to fall into the hands of an Al Qaeda affiliate.
Concerns over the rising power of Al Nusra has led the US, and its regional allies, to recently bolster material support for secular minded rebels in the FSA.