The announcement of the arrest of Salim Abdullah Ashur al-Shujayri, also known as Abu Othman, was a major breakthrough in a series of kidnappings. He was captured Aug. 11 in Baghdad and accused of being "the planner behind the kidnapping" of Carroll, a Christian Science Monitor reporter who was seized Jan. 7, 2006 and released three months later, the military said in a statement.

It said Shujayri's associates were also involved in the kidnappings of Christian peace activists and British aid worker Margaret Hassan, but did not elaborate.

It said U.S. troops also captured Ali Rash Nasir Jiyad al-Shammari on Aug. 17 in Baghdad. It described Shammari, also known as Abu Tiba, as a senior adviser for the terrorist network who funneled money, weapons and explosives to insurgents in the capital "during its most active operational period in early 2007."

News of the arrests was tempered by a suicide bombing yesterday that left at least 25 people dead. The bomber blew himself up in the midst of a celebration to welcome home a detainee released from U.S. custody, Iraqi officials said.

The attack occurred in one of several tents set up outside a house in the Abu Ghraib area on Baghdad's western outskirts, according to residents and police. It was unclear if the former detainee was among the casualties.

Residents and police said Ayyid Salim al-Zubaie, a local sheikh in the mainly Sunni area, had invited dozens to a banquet in honor of his son, who was released that day from Camp Bucca in southern Iraq.

Residents said the son had quarreled with al-Qaeda members while in detention and may have been the target of the attack. The guests also included several members of the local Awakening Council, a U.S.-allied group that has turned against al-Qaeda.

Also yesterday, the U.S. military said a 13-year-old girl wearing a bomb vest surrendered to Iraqi police in Baqubah rather than blow herself up.

Kidnappings forced foreigners to flee Iraq or take refuge in heavily guarded compounds, diminishing the ability of aid groups and journalists to operate. Many of the victims were butchered and their deaths recorded on videotapes distributed to Arab satellite TV stations or posted on the Web.

Hassan, 59, the director of CARE international in Iraq, was abducted in Baghdad in October 2004 and shown on a video pleading for her life, calling on British Prime Minister Tony Blair to withdraw troops from Iraq. She was killed a month later, but her body was never found.