WASHINGTON - The U.S. military is reinforcing the sides of its top mine-resistant vehicles to shore up what could be weak points, as troops experience a jump in armor-piercing roadside bombings across Iraq.

Navy Lt. Cmdr. James Hadley, who is overseeing the upgrades in Kuwait, said not every mine-resistant, ambush-protected vehicles, called an "MRAP," is getting the additional armor, which increases the vehicle's weight by as much as 5,000 pounds. The extra protection, he said, is being added to vehicles destined for hot battleground areas.

Army spokesman Paul Boyce said that commanders are increasing safety training to help troops better learn how to handle the heavy, ungainly vehicles.

The surge in attacks is putting the MRAPs to the test, and so far they are largely passing. Statistics reviewed by the AP show that while bombings involving the deadly penetrating explosives have jumped by about 40 percent in the past three months, deaths in such bombings have dropped by as much as 17 percent.

Officials attribute much of the decline in deaths to the increased use of MRAPs. To date, about a half-dozen service members have died in incidents that involved the new bomb-resistant vehicles, and several of those deaths occurred in rollovers rather than from explosives penetrating the armor.

The military shipped as many as 20 of the newly upgraded vehicles to the battlefront in April. An additional 30 are to go into Iraq beginning this month.