A U.S. soldier was killed in an attack by an armor-piercing roadside bomb Wednesday in Baghdad in a spike of violence that pushed to at least 10 the number of Americans who have died here this week.

The soldier was killed at about 9am in the predominantly Shiite eastern half of Baghdad, the military said.

The explosive device are believed to come from Iran and have been used by Shiite extremists to kill hundreds of American forces.

The U.S. military said three other American soldiers and an Iraqi interpreter were killed late on Tuesday by a roadside bomb in the northern Ninevah province, where al-Qaida in Iraq and other Sunni extremist groups remain active.

Destruction: Iraqi security forces secure the site of a bomb attack in Kerbala

Those fatalities brought the death toll for American troops in Iraq this month to at least 26 - well below figures of last year but an increase over the 19 who died in May, the lowest monthly tally of the war.

In all, at least 4,110 U.S. military service members have died in the Iraq war since it began in March 2003, according to an Associated Press count.

The U.S. military says violence in Iraq has dropped to its lowest level in more than four years but that attacks are continuing as Sunni and Shiite extremists try to regroup and undermine security gains.

"The level of violence has dropped dramatically," said Lt. Col. Steve Stover, spokesman for the U.S. command in Baghdad. "It has gotten quieter. But that doesn't make these losses any easier."

He said militants "are constantly thinking of ways that they can undermine us, undermine the government, undermine the Iraqi security forces."

The bombing in Nineveh occurred a day after a bombing in a district council office in the Baghdad Shiite district of Sadr City killed four Americans - two soldiers and two government employees.

Enlarge 

Blast alert: An Iraqi soldier stands guard at the scene of an explosion near the Imam Abbas shrine

The government employees were identified as Steven L. Farley of Guthrie, Oklahoma, a member of a provincial reconstruction team, and Nicole Suveges, a 38-year-old political scientist from Wauconda, Illinois, who was working with the military.

The Iraqi Defence Ministry spokesman suggested that the four Americans were not the main targets of the attack. Five Iraqis and an Italian-Iraqi interpreter for the Americans also were killed.

Maj. Gen. Mohammed al-Askari, the spokesman, said a preliminary investigation indicated that internal Shiite rivalries among the council members were to blame.

"The presence of the American forces and embassy employees was by chance," al-Askari said. "Chance played a role in the casualties among the Americans."

On Monday, a Sunni gunman waiting in a car killed two U.S. soldiers and an interpreter as they emerged from a meeting with municipal officials in Madain, about 15 miles southeast of Baghdad.

The U.S. military said American soldiers on Wednesday killed three suspected militants, including two women, after they came under small-arms from a vehicle near the Baghdad International Airport - one of the most heavily guarded areas in Iraq.

Atrocity: A bomb ripped through a bus near the revered Shiite shrine of Imam Abbas in the holy Shiite city of Karbala

The soldiers, who were part of a convoy that was stopped on the roadside, returned fire. That caused the vehicle to run off the road and explode, killing the three people inside, the military said.

But a security official at the hospital that received the bodies said the three people killed were bank employees and not militants. The official spoke on condition of anonymity because he said he was not authorized to release information.

U.S. soldiers acting on tips also found nine rockets in the back of a truck ready to be fired at a joint American-Iraqi base in the Shiite militia-dominated neighborhood of Hurriyah in northwestern Baghdad.

Col. William Hickman, the commander of the 2nd Brigade Combat Team, 101st Airborne Division that operates in the area, said the attack most likely would have "hurt many of our soldiers but it easily could have killed many innocent civilians also."

A car bomb also killed three people and wounded seven in Baghdad's Karradah district, witnesses and police said.

South of Baghdad, a bomb exploded on a minibus near one of the most revered Shiite shrines in the holy city of Karbala. At least two people including a young boy were killed, and 14 were wounded, police said.