Those arrested included former Brig. Gen. Abu Aymad al-Tikriti, former head of military intelligence in northern Iraq, Brig. Gen. Mark Kimmitt said. Al-Tikriti is suspected to have led a cell of anti-coalition insurgents.
Kimmitt, deputy chief of staff for operations, also said U.S. forces captured Majid Ali Abbas al-Dazi, suspected to have been involved in a suicide truck bombing Jan. 24 in the central town of Samarra that killed four Iraqi civilians and wounded about 40 people, including seven American soldiers.
U.S. troops also arrested a relative of Izzat Ibrahim al-Douri, and believe he may help in the hunt for the most senior former regime figure still at large, a U.S. officer said Wednesday.
Meanwhile, an Iraqi militant group claimed responsibility for the suicide bombings in Irbil.
In other developments:
On Tuesday, two suicide bombers blew themselves up at the offices of two Kurdish parties in the northern city of Irbil on Sunday, killing 109 people.
An Iraqi insurgent group, the "Jaish Ansar al-Sunna," claimed responsibility Wednesday, saying it targeted the "dens of the devils" because of the parties' ties to the United States. The claim could not be independently confirmed.
The two Kurdish parties are the strongest allies of the United States and had fought alongside its troops during the invasion of Iraq last March.
The statement claiming responsibility was posted in Arabic on a Web site that frequently carries statements by Islamic militants.
The name of the organization was included among a dozen insurgent groups that issued a joint statement this week in Ramadi and Fallujah — part of the Sunni Triangle stronghold of Saddam Hussein loyalists — warning Iraqis against cooperating with the U.S.-led occupation.
Kimmitt said U.S. authorities believe Jaish Ansar is a splinter group of Ansar al-Islam, an extremist group in northern Iraq with alleged ties to al Qaeda. He said he believed Jaish Ansar had also claimed responsibility for Saturday's car bombing at a Mosul police station, which killed nine Iraqis and injured about 45.
The attacks killed numerous officials of the Kurdistan Democratic Party and the Patriotic Union of Kurdistan. Insurgents have in recent weeks widened their operations to target Iraqi civilians besides U.S. forces, who have lost 368 troops to hostile fire since the invasion. The January toll was five more than in December.
Despite continuing losses, Maj. Gen. Raymond Odierno, commander of the Army's 4th Infantry Division based in Tikrit, predicted that coalition forces would be able to crush the insurgency within a year. He said the violence shows the insurgents are trying to sabotage a future government or gain leverage in it.
"There are ethnic issues. People are now positioning themselves to see what their role is in the next government, and they are doing it by force," Odierno said after a tour of Tikrit, Saddam's hometown.
The U.S.-led Coalition Provisional Authority plans to hand sovereignty to a provisional Iraqi government on June 30. However, Iraq's influential Shiite Muslim clergy wants a directly elected government rather than an administration chosen indirectly through a system of caucuses, as envisaged by Washington.
The United States says it is impossible to arrange elections as demanded by Shiite clerics in such a short time because of the ongoing insurgency.
L. Paul Bremer, the head of the Coalition Provisional Authority, said Thursday in Baghdad that a U.N. team will land in Baghdad "in coming days" to make recommendations to help end the deadlock. "The coalition will cooperate in any way the United Nations wants," Bremer told reporters.
He said although the date for handing over power remains unchanged, the United States is "prepared to consider refinements or elaborations" on an agreement holding caucuses.