Tikrit, Iraq ? A U.S. helicopter crashed in the Tigris river while searching for a missing soldier Sunday, and the aircraft’s two crew members were missing, the military said.

It did not say what caused the crash of the OH-58D Kiowa Warrior helicopter, attached to the 101st Airborne Division.

The helicopter was searching for a soldier missing when the boat he was in capsized earlier Sunday while on patrol. The other three soldiers in the boat were safe, but two Iraqi police officers and an Iraqi translator were confirmed killed in the incident, said Maj. Josslyn Aberle, a spokeswoman for the 4th Infantry Division.

She said the search for the two pilots was under way. U.S. troops and Iraqi police sealed off the area and established checkpoints to secure the search-and-rescue operation.

U.S. troops rushing to the scene came under “limited and ineffective small arms fire,” the spokeswoman said. An Iraqi policeman at one of the checkpoints was killed in a drive-by shooting, witnesses said.

It was the fifth helicopter crash in Iraq this month — three of them due to hostile fire.

Dozens arrested in raid

U.S. troops arrested nearly 50 people Sunday in raids in the Sunni Triangle after attacks in the volatile region killed six American soldiers.

Most of the arrests occurred in Baqouba, 35 miles northeast of Baghdad, where 46 people were detained in a series of raids, the U.S. military said. Three were arrested for alleged anti-coalition activities and the rest for illegal weapons possession.

Soldiers of the 4th Infantry Division also seized 220 hand grenades in a raid on a house in the town of Mukayshifa, south of Saddam Hussein’s hometown Tikrit, according to the spokeswoman.

The raids in the Sunni heartland followed a series of bombings and attacks Saturday in which six soldiers were killed. One of them, from the 4th Infantry Division, died Sunday of wounds suffered when insurgents fired a rocket propelled grenade at his Bradley vehicle in Beiji on Saturday.

Deadly weekend for troops

Five other U.S. soldiers were killed in two separate bombings Saturday in Khaldiyah and Fallujah, both located in the Euphrates River valley west of the capital. A blast Saturday in Samarra to the north of Baghdad narrowly missed an American convoy but killed four Iraqis and wounded about 40 others, including seven Americans.

A roadside bomb exploded Sunday near a U.S. patrol in Baghdad, but a U.S. soldier, speaking on condition of anonymity, said there were no U.S. casualties.

The latest deaths raised to 513 the number of U.S. service members who have died since the United States and its allies launched the Iraq war March 20.

Most of the deaths have occurred in the insurgency by Saddam Hussein loyalists since President Bush declared an end to active combat on May 1.