Muntasir Hamoud Ileiwi al-Jubouri and two of his aides were arrested in Muqdadiyah, 56 miles northeast of Baghdad late Friday, Brig. Qassim al-Mussawi, spokesman for the General Command of the Armed Forces, told The Associated Press.
He was arrested in Al-Taeyh, a village south of Muqdadiyah, al-Mussawi said. The General Command of the Armed Forces is the prime minister's military office.
Documents and assault rifles were seized with the three men, but no details were available.
Defense ministry spokesman Mohammed al-Askari told Iraqi state TV that he was arrested by soldiers from the 3rd brigade of the Iraqi army's 5th division.
The Sunni militant group has claimed responsibility for numerous suicide attacks, the August 2004 execution of 12 Nepalese hostages and a December 2004 explosion at a U.S. military mess hall in Mosul that killed 22 people. It is believed to have been an offshoot of another group, Ansar Al-Islam.
That group is made up mostly of Kurds with close links to al Qaeda and has been blamed for a number of attacks, including assassination attempts against Kurdish officials.
Ansar al-Sunna is part if the Mujahedeen Shura Council, an umbrella organization of insurgent groups — including al Qaeda in Iraq — that was co-founded by the late Jordanian-born terrorist mastermind Abu Musab al-Zarqawi.
In the Sadr City attack, another 38 people were wounded by the 10 a.m. blast in the sprawling Shiite slum. People frantically carried survivors from the narrow muddy street to ambulances, and hauled away bodies in blankets.
The bomb was hidden in a barrel near the tanker, where scores of people were waiting to buy fuel, said police Col. Saad Abdul-Sada.
A crowd of people was gathered behind the truck, with a long line down the street when the bomb exploded, Abdul-Sada said. There were more people on hand than usual as families sought to stock up on fuel for the Muslim holy month of Ramadan, he said.
In the aftermath of the blast, sandals of all sizes littered the ground, scattered around a large pool of water mixed with blood.
"I swear to Allah that this is a revenge against Sadr City," a young man yelled, raising his hands in the air. "Where is (Prime Minister Nouri) al-Maliki's government?"
Seventeen women were among the dead, Abdul-Sada said, adding that casualties were expected to rise.
Sadr City is home to more than two million people and a stronghold of the Mahdi army — a Shiite militia loyal to radical cleric Muqtada al-Sadr.
Baghdad has been a center for sectarian violence, with both Sunni Arab and Shiite death squads roaming the streets of the capital
The attack came a day after a death squad gunned down four people in an assault on Sunni Arab homes and mosques on the Muslim holy day in a neighborhood where a Shiite militia last week openly threatened members of the minority.
Iraq is approximately 60 percent Shiite, 20 percent Kurdish and 15 to 20 percent Sunni Arab.
In Kut on Saturday, 100 miles southeast of Baghdad, five apparent death squad victims were turned in to the morgue.
The bodies were shot in the head and chest and had been found dumped into the Tigris river near Suwayrah, 25 miles south of the capital, said morgue official Ma'moun Ajeel al-Rubai'ey.
The victims were blindfolded with their arms and hands bound, and showed signs of torture, he said.