BAGHDAD — A group of gunmen in two cars attacked a minibus heading to Baghdad from a Shiite town north of the capital today, killing seven passengers including a child, police said.

Meanwhile, thousands of soldiers continued their search for three comrades abducted in a May 12 ambush south of Baghdad. Four other U.S. soldiers and one Iraqi were killed.

The minibus attack underscored the sectarian violence and instability that continues to plague Diyala province north of Baghdad despite the three-month-old security crackdown in Baghdad and the surrounding areas.

The bus, which left the town of Khalis, was driving near the violence-wracked city of Baqouba, 35 miles northeast of Baghdad, about 11:30 a.m. when it was ambushed outside the town of Hibhib, police said.

In western Baghdad, a roadside bomb detonated near a group of Iraqi soldiers patrolling the Sunni-dominated Adil neighborhood, killing three soldiers and injuring two others.

The stepped-up U.S. and Iraqi patrols of the capital during the crackdown have left the troops more vulnerable to attack by insurgents, military officials say.

The U.S. military reported Sunday that six U.S. soldiers on patrol in Baghdad were killed in a roadside bombing along with their interpreter on Saturday. A seventh soldier died in a blast Saturday in Diwaniya, a mostly Shiite city 80 miles south of the capital, where radical Shiite militias operate.

Those deaths brought the number of American troops killed in Iraq since Friday to at least 15. So far, at least 71 U.S. forces have died in Iraq this month — most from bombs.

On Sunday, two U.S. Republican senators at an international conference hosted by the Geneva-based World Economic Forum in Jordan said that the U.S. has evidence Iran sent weapons and trainers to instruct militants in Iraq to carry out terror attacks.

Republican Sen. Orrin Hatch told a panel discussion on Iraq's future that during a trip last week to Iraq, he saw "evidence that Iran was supplying weapons and bomb-making components to Iraqi terrorists."

A former Iranian government official, who was on the same panel, denied the claims.

"Iraq is already so full of arms that it doesn't need arms from Iran," said hard-liner Mohammed J.A. Larijani, brother to Iran's top nuclear negotiator, Ali Larijani.

But Republican Sen. Gordon Smith said he saw "confiscated Iranian weapons" and captured Iranians who confessed to a mission to train Iraqi extremists in military tactics.