Iraqi army soldiers patrol a street in Baghdad's Shiite enclave of Sadr City, Iraq, on Monday. Iraqi troops in Sadr City set up checkpoints and took a far more visible presence than the U.S. forces, who led the push into the area Sunday. While the security crackdown in Baghdad has reduced violence there, north of the capitol nine U.S. soldiers were killed and at least three wounded Monday in two separate bombings.

BAGHDAD, Iraq — Nine American soldiers died in explosions north of Baghdad, the U.S. military announced today after the deadliest single day for U.S. troops in Iraq in nearly a month.

Six soldiers died when a bomb exploded Monday near their vehicles during a combat operation in Salahuddin province, the military said. Three others were wounded in the blast.

Another three soldiers died the same day in a roadside bomb attack in Diyala province northeast of Baghdad.

Shiite pilgrims, too, came under attack as they streamed south, mostly on foot, toward a shrine in Karbala ahead of a weekend holiday. Police said at least 20 were killed today in shootings and bombings along the way.

In Baghdad, U.S. forces continued their push into Sadr City, home to 2.5 million of the city's poorest residents as well as fighters loyal to anti-American cleric Muqtada al-Sadr. Some 600 American soldiers searched the neighborhood's northwest quadrant, knocking on doors and searching homes, according to an Associated Press reporter traveling with them.

The U.S. forces are seeking a "reconciliatory approach" to avoid sparking a backlash on the streets, said Col. Richard Kim. One small gesture seemed to offer appreciation: a child offering soldiers ice cream bars.

Monday was "a very traumatic day" for U.S. troops in Iraq, said Lt. Col. Michael Donnelly, a spokesman for U.S. forces in northern Iraq.

"Our hearts and prayers are with the families right now in their time of loss, and our resolve is stronger to accomplish our mission here," Donnelly said.

Both provinces where Monday's deaths occurred are Sunni-dominated. Saddam Hussein's clan hails from Salahuddin, and the late al-Qaida in Iraq leader Abu Musab al-Zarqawi was hiding out in Diyala when he was killed by a U.S. airstrike there last summer.

Violence has fallen in Baghdad, where a joint U.S.-Iraqi security crackdown was in its third week. But U.S. military officials say insurgents have fled the capital for outlying areas, where attacks are on the rise. Direct attacks on U.S. forces in Diyala are up 70 percent since last July, according to figures provided by the U.S. military.

A suicide car bomber shattered the capital's relative calm Monday, striking a famous book market in the city's oldest quarter and killing at least 38 shoppers.

At least 20 Shiite Muslims were killed on their trek southward today toward Karbala, where they would mark the end of a 40-day mourning period after the death of the Prophet Muhammad's grandson.

The deadliest attack was in the south Baghdad neighborhood of Dora, where gunmen pumped bullets into a minibus, killing all eight passengers inside, police said. A car bomb nearby killed two others hours later, they said.