An American citizen has been reported missing in Iraq, the U.S. Embassy said Monday, a day after a Canadian Parliament official said that four humanitarian workers had been kidnapped.

Dan McTeague, parliamentary secretary for Canadians abroad, said two Canadians were taken on Saturday, and Britain said one of its citizens was among the four.

U.S. Embassy spokeswoman Elizabeth Colton said only that an American had been reported missing. The person's name was not immediately released.

McTeague refused to name the organization the two Canadians worked for or the location where they were kidnapped in order to protect the safety of the individuals involved.

Briton Norman Kember was among the four, the British government said Sunday. His wife said he was representing a number of groups in the country and was a longtime peace activist.

Most international organizations fled Iraq last year following a wave of kidnappings and beheadings of foreign and Iraqi hostages. Many of them were carried out by Al Qaeda in Iraq, led by the Jordanian Abu Musab al-Zarqawi.

Meanwhile, two Britons were killed and three injured Monday when gunmen attacked a bus carrying Muslim pilgrims south of Baghdad, police and hospital officials said.

The gunmen attacked the bus when it neared a checkpoint in the Dora neighborhood, police Capt. Talib Thamir said. The bus was carrying Shiite Muslim pilgrims to religious sites south of the capital, he said.

Four men and one woman, apparently of South Asian heritage and carrying United Kingdom passports, were taken to Baghdad's Yarmouk hospital, an official there said.

"We were just coming and all of a sudden heard shots and immediately got down," said an injured British woman, who identified herself as Z. Jafferti. "I don't know what happened and I couldn't see anything."

She said she had been ill and had come to Iraq to pray at the shrines to Imam Ali and Imam Hussein.

Also Monday morning, a mortar shell fell in central Baghdad's Green Zone and two others fell nearby, just hours before Saddam Hussein's trial was set to begin. There were no report of injuries from the shelling, police Lt. Bilal Ali Majeed said.

A roadside bomb also detonated next to a passing U.S. Army convoy in northeastern Baghdad Monday, setting fire to a Bradley fighting vehicle. Police Capt. Mohammed Abdul-Ghani said three soldiers were injured, but no other information was immediately available.

The U.S. military reported that a Marine assigned to the 2nd Marine Aircraft Wing was killed Saturday when his vehicle struck a roadside bomb near Camp Taqaddum, 45 miles west of Baghdad. At least 2,106 U.S. military personnel have died since the Iraq war started in March 2003, according to an Associated Press count.

Near Kirkuk, 180 miles north of Baghdad, soldiers from the 101st Airborne Division found more than 2,700 mortar rounds buried near an abandoned Iraqi Army base, a U.S. statement said. Troops were excavating similar mounds Monday in search of more weapons.

In an interview published Sunday, Ayad Allawi, a secular Shiite Muslim, told the London newspaper The Observer that fellow Shiites are responsible for death squads and secret torture centers and said brutality by elements of Iraqi security forces rivals that of Saddam's secret police.

"People are remembering the days of Saddam. These were the precise reasons that we fought Saddam and now we are seeing the same thing," the newspaper quoted Allawi as saying.

Allawi's allegation of widespread human rights abuses follows the discovery this month of up to 173 detainees, some malnourished and showing signs of torture, in a Shiite-led Interior Ministry building in Baghdad.

"People are doing the same as Saddam's time and worse," he said. "It is an appropriate comparison."

His remarks appeared aimed at winning favor among the Sunni Arab minority as well as secular Shiites ahead of the Dec. 15 parliamentary elections. Allawi is running on a secular ticket that includes several prominent Sunnis.

During his tenure as prime minister, Allawi lost the support of many Shiites because he brought former members of Saddam's Sunni-dominated regime back into the security services to bolster the fight against insurgents.

There was no comment from Shiite politicians on Allawi's interview. However, the leader of Iraq's biggest Shiite party said allegations of torture were distortions and might be designed to draw attention away from the Saddam's trial, which resumed Monday after a five-week break.