The head of Syria's jihadist Al-Nusra Front pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri on Wednesday, but distanced his group from claims it had merged with Al-Qaeda in Iraq.
The announcement is likely to bolster assertions by the regime of Syrian President Bashar al-Assad that it is fighting "terrorists" who want to impose an Islamic state, and could further complicate Western attempts to help rebel forces.
"The sons of Al-Nusra Front pledge allegiance to Sheikh Ayman al-Zawahiri," Abu Mohammed al-Jawlani said in the recording.
But, he added, "we were not consulted" on an announcement by Al-Qaeda in Iraq chief Abu Bakr al-Baghdadi on Tuesday of a merger with Al-Nusra Front.
"We inform you that neither the Al-Nusra command nor its consultative council, nor its general manager were aware of this announcement. It reached them via the media and if the speech is authentic, we were not consulted," Jawlani said.
He added that the group would not be changing its flag or its "behaviour".
"Al-Nusra Front will not change its flag, though we will continue to be proud of the flag of the Islamic State of Iraq, of those who carry it and those who sacrifice themselves and shed their blood for it," said Jawlani, acknowledging he had fought in Iraq alongside the ISI, Al-Qaeda's Iraqi branch.
"We reassure our brothers in Syria that Al-Nusra Front's behaviour will remain faithful to the image you have come to know, and that our allegiance (to Al-Qaeda) will not affect our politics in any way," he added, keen to assert the group's autonomy.
Jawlani's comments came a day after the ISI made a surprise announcement that Al-Nusra was part of its network, confirming long-held suspicions that led the United States to put the Syrian jihadist group on its terror blacklist.
"It is time to declare to the Levant and to the world that the Al-Nusra Front is simply a branch of the Islamic State of Iraq," ISI chief Baghdadi said in an audio message.
The groups would be combined and called the Islamic State in Iraq and the Levant, Baghdadi said, describing Jawlani as "one of our soldiers".
The announcement followed a message from Zawahiri, urging rebels to fight to establish an Islamic state in Syria, and was received with caution by the mainstream rebel Free Syrian Army.
"We don't support the ideology of Al-Nusra," FSA spokesman Louay Muqdad told AFP, stressing: "There has never been and there will never be a decision at the command level to coordinate with Al-Nusra.
The group is among the most prominent organisations involved in Syria's conflict, which erupted in March 2011 with peaceful protests against Assad's regime but has evolved into a war that has killed tens of thousands.
The Islamist militant group has gained notoriety for its suicide bombings but also won admiration from some insurgents for its reputation as a formidable fighting force leading attacks on battlefronts across Syria.
The West has been wary, and the announcements this week are likely to complicate any attempt to arm the rebels.
On Wednesday, Syrian rebels are meeting US Secretary of State John Kerry and G8 foreign ministers in London to push for weapons shipments.
The US and EU are currently providing non-lethal aid to the rebels, but Britain and France want an EU arms embargo on Syria lifted so they can supply the rebels with weapons.
But many countries have refused to arm the opposition fearing the weapons could get into the hands of Al-Qaeda-linked militants.
In Syria on Wednesday, Kurdish fighters expelled regime troops from part of the majority Kurdish city of Hasake, the Syrian Observatory for Human Rights reported.
Elsewhere warplanes raided the outskirts of Damascus, where rebels have established rear bases from which they are targeting th capital.
At least 162 people were killed in violence throughout Syria on Tuesday, the Observatory said. Among them were 23 civilians, 81 rebels and 58 soldiers.