Baghdad, Iraq ? Iraqi authorities pulled a brigade of about 700 policemen out of service Wednesday in the biggest move ever to uproot troops linked to death squads, aiming to signal the government’s seriousness in cleansing Baghdad of sectarian violence.

The government move came amid steadily mounting violence, particularly in the capital. A U.S. military spokesman said the past week had seen the highest number of car bombs and roadside bombs in Baghdad this year.

Four U.S. soldiers patrolling in Baghdad were killed by gunmen Wednesday, the U.S. military said, also announcing the deaths of two other soldiers a day earlier in Baghdad and the northern city of Kirkuk. The deaths brought to 21 the number of Americans killed in combat since Saturday, and the toll since the war started in March 2003 to 2,736.

The suspension of the police brigade was the first time the Iraqi government has taken such dramatic action to discipline security forces for possible links to militiamen, though some individual soldiers have been investigated in the past. Baghdad’s Sunnis widely fear the Shiite-led police, saying they are infiltrated by militias and accusing them of cooperating with death squads who snatch Sunnis and kill them.

The brigade was responsible for a region of northeast Baghdad with a slight Shiite majority, where gunmen Sunday kidnapped 24 workers from a frozen food factory. Hours later, the bodies of seven of the workers were found dumped in a district miles away.

Sunni politicians have said all those who were kidnapped were Sunnis. They blamed Shiite militias for the abduction and accused police of allowing the gunmen to escape and move freely with their captives.

Brig. Abdul-Karim Khalaf, the chief ministry spokesman, said the brigade was being investigated because it “didn’t respond quickly” to the kidnapping.

The top U.S. military spokesman in Iraq, Maj. Gen. William B. Caldwell, said the police brigade in the area had been ordered to stand down and was undergoing retraining. He said some were being investigated and that any found to have militia ties would be removed.

“There is clear evidence that there was some complicity in allowing death squad elements to move freely when, in fact, they were supposed to have been impeding their movement,” Caldwell said.