BAGHDAD - A suicide bomber struck a police station northeast of Baghdad yesterday, killing four officers two days after a double truck bombing killed nine U.S. soldiers in the volatile area.

Explosions, shootings and mortar attacks left at least 41 people dead elsewhere.

The attacker blew himself up at the front gate of the station in Balad Ruz, 50 miles northeast of Baghdad, police said. Sixteen people, including 11 civilians, were wounded.

Balad Ruz is in Diyala province, which has seen some of the worst violence recently as mostly Sunni militants are believed to have fled to the area since U.S. and Iraqi troops launched a security crackdown in Baghdad on Feb. 14.

An al Qaeda-linked group claimed responsibility for Monday's double-suicide suicide bombing in which two dump trucks blasted a paratrooper outpost in Diyala province, causing the two-story building to collapse, killing the U.S. troops.

U.S. commanders hope to minimize such bombings in the capital by constructing walls around neighborhoods that have been wracked by sectarian killings.

Last week, the U.S. military announced it was building a 3-mile-long, 12-foot-high concrete wall in Azamiyah, a Sunni stronghold that has been targeted by mortar and rocket attacks by Shiite militiamen.

But the announcement drew sharp criticism from many Azamiyah residents, who denounced the plan as an attempt to isolate Sunnis.

In a statement yesterday, the Sunni Conference for the People of Iraq accused the government of ignoring "the return of the militias and death squads to target Sunni areas" and said building walls was designed to make Sunnis "soft targets for militias."

Yesterday radical Shiite cleric Muqtada al-Sadr joined in the criticism, saying the wall was a "sectarian, racist and unjust" plot by the Americans to divide Iraqis.

Al-Sadr's Mahdi militia has been blamed for much of the sectarian bloodshed the U.S. says the Azamiyah wall is designed to stop.

Also yesterday, the U.S. military said an American soldier died Tuesday in a noncombat-related incident. No further details were released.

Meanwhile, U.N. officials accused Iraq of withholding civilian death figures to deflect attention from escalating violence and a worsening humanitarian crisis despite the security crackdown.

Those conclusions by the U.N. Assistance Mission for Iraq drew a sharp rebuke from the Iraq's political leadership, which called the report "unbalanced" and said it raised questions about the credibility of the U.N. staff in Iraq.

"Armed groups from all sides continued to target the civilian population," the report said.

It also took issue with tactics used against Iraqi civilians in Baghdad - alleging, for example, that whole families were often taken into custody at random during security sweeps. The study's critical tone emboldened the vote by the Democratic-controlled Congress to begin withdrawing U.S. troops by Oct. 1. *