Iraq's al Qaeda wing has united with a kindred Syrian group in the frontline of a struggle to oust President Bashar al-Assad, sharpening a dilemma for nations that back the revolt, but fear rising Islamist militancy.
The leader of the Islamic State of Iraq, Abu Bakr al-Baghdadi, said his group had trained and funded fighters from Syria's al-Nusra Front - which is blacklisted by the United States - since the early days of the two-year-old uprising.
He said in a statement posted on Islamist websites and seen by Reuters on Tuesday that the two groups would operate under the joint title of the Islamic State of Iraq and the Levant.
"It's now time to declare in front of the people of the Levant and the world that al-Nusra Front is but an extension of the Islamic State of Iraq and part of it," Baghdadi said.
"We thus declare ... the cancellation of the name of the Islamic State of Iraq and the name of al-Nusra Front and grouping them together under one name, the Islamic State of Iraq and the Levant," he added.
The militant Islamist element of the Syrian conflict poses a quandary for Western powers and their Arab allies, which favour Assad's overthrow but are alarmed at the growing power of Sunni Muslim jihadi fighters whose fiercely anti-Shia ideology has fuelled sectarian tensions in the Middle East.
A US analyst said the announcement was no game-changer, but reflected al Qaeda's confidence in its position in Syria.
"I don't think it necessarily changes anybody's calculus since ... the United States already knew about this connection last year and there hasn't been any change in policy per se by the United State or its allies in Syria in the last six months," said Aaron Zelin, of the Washington Institute for Near East policy.
Baghdadi's statement, first reported by the US-based SITE monitoring service, could not immediately be authenticated, and there was no immediate comment from al-Nusra on the merger.
Baghdadi said his group had deployed battle-hardened fighters and sent funds to local al-Nusra cells set up in Syria to lay the groundwork for the armed uprising - which grew out of anti-Assad protests that erupted in March 2011 - but that it had refrained from announcing the link for security reasons.
The Front burst into prominence early last year, when it claimed responsibility for several powerful bombings in the Syrian capital Damascus and the northern city of Aleppo.