Hussain Kamal, the deputy interior minister, said that al-Zarqawi was "arrested more than a year ago in Falluja by Iraqi police". He said: "It seems they did not recognise him, that's why they released him."
Al-Zarqawi, 39, is allegedly the frontman of al-Qaida in Iraq and the mastermind of numerous bombings, armed attacks, hostage murders and other acts of violence in the country.
The Jordanian Islamist is Iraq's most wanted man and has a $25million US bounty on his head. He has only one leg after being injured fighting for the Taliban in Afghanistan.
He has been sentenced to death in Jordan for the murder of a US diplomat in 2002.
"He got away once, he will not get away the next time," Kamal said. "He will be tried for the crimes he committed against the Iraqi people."
US military forces in Iraq have claimed to have killed or captured a number of al-Zarqawi's top operatives and said they have come close to capturing al-Zarqawi himself on a number of occasions.
Major-General Rick Lynch, a spokesman for the US-led multinational force in Iraq, said last month: "We come close to Zarqawi continuously and at one point in time, in the not too distant future, we are going to get Zarqawi."
Unlike Osama bin Laden, al-Zarqawi has never released a videotaped message.
Only grainy identity shots, old images from Afghanistan and more recent photos of a portly, grizzled figure give any clue as to his appearance.