BAGHDAD - Teenagers armed with grenades and suicide vests are the latest recruits for Sunni insurgents trying to find new ways to outwit heightened security measures and attack American and Iraqi forces, the U.S. military said yesterday.

The use of boys also serves a propaganda purpose - soldiers face criticism for harming children if they fire back.

Insurgents first turned to women to carry out suicide bombings, prompting U.S. and Iraqi troops to step up recruiting and training of female operatives to search women at checkpoints to look for explosives easily hidden under robes.

Now they appear to be using youths and weapons such as grenades that are easier to hide as they face omnipresent checkpoints and convoys aimed at bolstering security gains that have caused the level of violence to plummet nationwide.

"With grenade attacks, insurgents hope to capitalize on reports of civilian injuries blamed on a coalition response to the attack," said Maj. Derrick Cheng, a spokesman for U.S. forces in northern Iraq. "However, the reality is that the grenade explosion itself causes the majority of civilian casualties."

The military has said it believes al-Qaeda in Iraq and other insurgent groups are recruiting children because of their ability to avoid scrutiny.

But a statement issued yesterday was the first to provide detailed allegations of teenage suspects in what the military called "a growing trend of children carrying out attacks on Iraqi security and U.S. forces."

Cheng stressed that roadside bombs were still the main mode of attack against U.S. forces but said grenades were often the weapon of choice in urban areas where it is harder to plant explosives without being seen.

Young men can quickly throw grenades and fade into crowds, depriving soldiers of the chance to fight back amid fears that they will hit innocent civilians. The tactic has been used in fighting before but takes on added significance as Americans have been trying to improve relations with the Iraqi public in a bid to stem support for the insurgency.

Army Col. Gary Volesky, who commands U.S. troops in northern Iraq's Ninevah province, said that grenade attacks were on the rise but that a "more disturbing trend" was the recruiting of children to throw them.

On May 9, U.S. soldiers killed a 12-year-old boy who the military said was believed involved in a grenade attack in the northern city of Mosul. Local residents said he was an innocent civilian. But the military said the boy was found with 10,000 dinars, or about $9, in his hand, which they said suggested he had been paid by insurgents.