The Iraqi Red Crescent shut its Baghdad branches on Monday, a day after gunmen seized 30 of the aid group's workers and volunteers, and the U.S. military announced the deaths of two more American troops.

Sixteen guards, drivers and other workers, along with two visitors and three guards from the neighboring Dutch Embassy, were released after several hours in captivity, a Red Crescent spokesman said on condition of anonymity because of security concerns.

"We gave orders to our Baghdad staff to stop working till further notice. We renew our calls for the release of the kidnapped persons," said Mazin Abdellaha, the Iraqi Red Crescent's secretary-general.

He said the group's offices in other Iraqi provinces were still operating.

On Monday afternoon, a car bomb exploded near a vegetable market in southwest Baghdad, killing five people and wounding at least 14, police said.

The blast occurred at a green grocers' wholesale depot around 1:15 p.m. local time in Sadiyah, a primarily Sunni area of the Iraqi capital, officials said.

Also Monday, an Iraqi official said Ayham al-Samaraie, a former electricity minister who holds dual U.S.-Iraqi citizenship, escaped from police custody.

Al-Samaraie, who was convicted in October of corruption and sentenced to two years in prison, escaped Sunday with help from members of a security company he had hired to protect him before his arrest, said Faris Kareem, deputy head of Iraq's Public Integrity Commission.

Kareem said the security agents were "foreign," but he had no further details.

Visit FOXNews.com's Iraq Center for more in-depth coverage.

The weekend deaths of a Marine and soldier in Iraq's western Anbar province raised to 59 the number of American troops killed in December. The Marine, assigned to Regimental Combat Team 5, died Saturday, and a soldier with the U.S. Army's 1st Brigade, 1st Armored Division died Friday, the military said.

Both names were withheld pending notification of families.

At least 2,947 members of the U.S. military have died since the U.S.-led invasion in March 2003, according to an Associated Press count.

The Iraqi Defense Ministry said that the government did not know who was behind the Red Crescent kidnappings, but said they were likely "the same groups" responsible for similar attacks in recent months.

"They aim at paralyzing life and stopping government and social life," spokesman Mohammed al-Askari said. "Targeting the Red Crescent is a horrible act."

Police said the gunmen arrived at the Red Crescent office Sunday in five pickup trucks. Red Crescent officials had initially said 25 employees were kidnapped, but a spokesman said Monday that 30 employees and volunteers were seized.

Many international aid organizations closed down their operations in Iraq as the security situation deteriorated after the U.S.-led invasion that ousted Saddam Hussein.

The Red Crescent, which is part of the international Red Cross movement, has around 1,000 staff and some 200,000 volunteers in Iraq. It works closely with the International Committee of the Red Cross, which visits detainees and tries to provide food, water and medicine to Iraqis.

The ICRC's director of operations, Pierre Kraehenbuehl, said the Red Crescent was the only aid organization able to work throughout Iraq — the only country where the ICRC, whose Baghdad headquarters was bombed in 2003, travels incognito for fear that its symbol could be taken as a target by armed groups rather than an emblem of protection.

At least half a dozen mass kidnappings have been carried out in the Iraqi capital this year, possibly by armed groups linked to the sectarian conflict between Sunnis and Shiites.

In other violence Monday:

— Police discovered four bodies that had been blindfolded, handcuffed and shot execution-style off an expressway in western Baghdad.

— A roadside bomb missed a police patrol on a busy thoroughfare in eastern Baghdad but killed one bystander and wounded two others, police said. Two mortar shells killed one person and injured two others in a house in southwest Baghdad, and a bomb injured five people in a civilian car in the southwestern suburbs.

— A sniper killed a guard at the gate of the University of Technology in downtown Baghdad, police said. This month, a a Sunni Arab insurgent group warned university professors and students to avoid classes while it cleanses campuses of Shiite death squads, but Prime Minister Nouri al-Maliki urged them to ignore the threat.

— In northern Iraq, a member of the Nineveh provincial council, Khairi al-Dabagh, was shot dead on his way to work, police said. The Sunni Arab politician was killed in Mosul, 225 miles northwest of Baghdad.

— Police in Diyala province, east of Baghdad, said gunmen killed two civilians and wounded another near Baqouba, the provincial capital. A roadside bomb detonated north of Baqouba, killing an Iraqi soldier and wounding another.

The U.S. military announced Monday that coalition forces had killed four insurgents and detained two others north of Baghdad on Friday. The insurgents were setting up ambush positions along the main highway between Baghdad and Mosul when U.S. forces engaged them, the military said.

Coalition forces seized weapons including three AK-47s and three rocket-propelled grenade launchers.

Visit FOXNews.com's Iraq Center for more in-depth coverage.