BAGHDAD — U.S. military deaths in Iraq increased by about one-third in the past year, even as Iraq established its own government and assumed more responsibility for battling the insurgency.
At least 882 U.S. troops died in the 12 months through Thursday, up from 657 in the preceding year, according to a USA TODAY analysis of Defense Department numbers. Iraqis assumed sovereignty a year ago this week, part of a U.S. strategy to lessen the visibility of U.S. troops and shift more responsibility for security to Iraq forces.

Lately, insurgents have made roadside bombs deadlier and deployed more car and suicide bombs.

Marine Lt. Gen. James Conway said at a Pentagon briefing Thursday that insurgents are increasing their use of the type of attack "that gives you the big blast and possibly causes more casualties."

"The insurgency is shifting all the time," Maj. Gen. William Webster, commander of U.S. troops in Baghdad, said recently. "This is a learning enemy."

In June, 79 U.S. servicemembers died in Iraq, about as many as in May.

President Bush has counseled patience with the mission. In marking the anniversary of sovereignty Tuesday night, he warned that there will be "tough moments that test America's resolve" in Iraq.

The insurgents' continually shifting tactics have frustrated U.S. and Iraqi military efforts to halt their attacks. For example, offensives in Fallujah and other insurgent strongholds deprived the militants of havens and forced them to scatter them throughout the country. The insurgents then regrouped in scattered pockets. The increasing use of car bombs may be part of the insurgents' reaction to the offensives that took away their secure bases.

Car bombs inflict maximum damage with minimum resources, Air Force Brig. Gen. Donald Alston, the chief U.S. military spokesman in Iraq, said Thursday.

"They've gone to more spectacular systems that could inflict more casualties per attack, likely because they can't sustain a high volume of attacks," Alston said.

The military cautions against drawing conclusions from spikes in violence. Attacks typically come in waves, and militants use the lulls between those waves to regroup, train and choose new targets.

For example, there were a record 140 car bombs in May and 135 in April. In June, the number dropped to 70, plus 18 that were discovered before they were detonated, according to the U.S. military.

Insurgents have also created more dangerous roadside bombs designed to penetrate the American military's heavily armored vehicles. "Shaped charges" are designed to concentrate the blast in a single area, increasing the chance of penetrating armor.

"We have lost soldiers and/or Marines to some of these devices," Conway said at an earlier briefing.

U.S. troops continue to train Iraqi forces. There are currently more than 168,500 trained and equipped Iraqi security forces, though not all are battle-ready.

Contributing: Steven Komarow in Washington