The Iraqi army arrested the alleged military leader of Al-Qaeda's offshoot in Iraq, Mikhlif Mohammed Hussein al-Azzawi, in an early morning raid on Wednesday, the defence ministry said.
The accused insurgent, also known as Abu Radhwan, was detained along with three other suspected leaders of the Islamic State of Iraq, spokesman Major General Mohammed al-Askari told AFP.
Also among those arrested were one of the men behind a deadly assault on a government building in northern Iraq in March and the head of the insurgent group's assassinations cell.
"These are four major leaders of Al-Qaeda in Iraq, and they are four of the most dangerous, most wanted figures of Al-Qaeda," Askari said.
He said the operation to detain the group was carried out by the Iraqi army at around 1:30am (2230 GMT) on Wednesday, west of Samarra, 110 kilometres (70 miles) north of Baghdad.
The others arrested were Mohammed Saad Muzzaham al-Daraji, the head of the Al-Qaeda branch's assassinations unit, Fawzi Abbas Ali al-Badri, who is also known as Abu Abdulrahman and was primarily charged with kidnapping soldiers with a view to killing them and burning their bodies.
Soldiers also detained Qassim Mohammed Taha, who is wanted in connection with a brazen 29 March attack in the city of Tikrit, north of Baghdad, in which 58 people were killed and 97 wounded.