TV network Al-Arabiya ran an alleged photograph of the little-known leader
Iraqi Prime Minister Nouri Maliki has said that a man arrested in Baghdad last week is a top figure in the al-Qaeda-related insurgency.
Mr Maliki told the BBC Abu Omar al-Baghdadi had been tracked for more than two months by Iraqi security services.
His arrest was reported last Thursday but the reports were not confirmed.
Al-Baghdadi is a nom de guerre for a shadowy figure thought to lead the Islamic State in Iraq, an umbrella group of radical Sunni militant groups.
In an exclusive interview with the BBC's Jim Muir in Baghdad, Mr Maliki disclosed that a purely Iraqi intelligence operation had tracked the wanted man's movements from the inside.
Nom de guerre
He had been identified by former close associates who had worked with him, and attended his inauguration as leader of the Islamic State in Iraq, an umbrella organisation of which al-Qaeda in Iraq is part.
Jim Muir, BBC correspondent in Baghdad
With around 150 people killed in just two days this week, Iraqis are wondering whether the latest attacks herald a return to those black times.
Nobody can be sure that they don't.
But so far, they are a blip on the screen - a big blip, but not one that takes the country anywhere near back to the levels of violence prevailing two years ago.
Prime Minister Maliki said al-Baghdadi was being interrogated, and that the results would be made public.
Abu Omar al-Baghdadi is a shadowy figure - some US commanders have even cast doubt on his very existence, our correspondent says.
The name is a nom de guerre - Iraqi officials say his real name is Ahmad Abid Ahmad Khamis al-Majmai, though he has also been known under other names.
The capture or killing of other senior al-Qaeda or related leaders in the past has not on its own made a perceptible difference to the state of the insurgency, our correspondent adds.
The arrest of Baghdadi on Thursday came amid an upsurge of the violence in Iraq.
About 150 were killed in just two days, sparking fears of a slide back into the bloody chaos that was a hallmark of Iraq following the US-led invasion.
Meanwhile on Sunday, a woman was shot dead during a US raid on a house in the southern Iraqi town of Kut in which at least five people were arrested.
The US military said she had been nearby during the operation, and had moved into the line of fire.
But the death was condemned as a crime by the local provincial council, and hundreds of people gathered at the local morgue to protest, reported the Associated Press news agency.