The leader of al-Qaeda in Iraq, Abu Ayyub al-Masri, has been arrested, according to media reports quoting the country's defence ministry.
Masri, also known as Abu Hamza al-Muhajir, was detained in the northern Iraqi city of Mosul, the reports said.
There has so far been been no official US or Iraqi confirmation.
The Egyptian-born militant took over the leadership of the group from Abu Musab al-Zarqawi shortly after he was killed in a US air strike in June 2006.
Masri is believed to have helped Zarqawi form the first al-Qaeda cell in Baghdad following the US-led invasion in 2004.
After becoming leader, he vowed to "continue what Sheikh Abu Musab began" and avenge his death with attacks that would "turn your children's hair white".
In April 2007, he was named "minister of war" in the 10-man cabinet of the Islamic State of Iraq, an umbrella organisation of Sunni militant groups.
Shortly afterwards, the Iraqi government claimed Masri had been killed in an "internal battle" between militants, but this was quickly denied by the group.
In an hour-long audio tape broadcast last month, he purportedly called for renewed attacks on US troops and noted the recent announcement that 4,000 had died in Iraq.
"We must celebrate this event in our special way, and make the defeated Bush join us in this celebration," he said.
(BBC)
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