Insurgents are increasingly using teenagers to stage attacks against American and Iraqi security forces, the U.S. military said Saturday.

At least five suspects ages 14 to 19 have been involved in grenade and suicide attacks in recent weeks in northern Iraq, according to the statement.

The military has frequently said it believes Al Qaeda in Iraq and other insurgent groups are recruiting children and women because of their ability to avoid scrutiny and evade heightened security measures.

But Saturday's statement was the first to provide detailed allegations of specific teenage attackers in what the military called "a growing trend of children carrying out attacks on Iraqi security and U.S. forces."

It said a teenage boy threw a grenade at a joint U.S.-Iraqi patrol in Hawijah, west of the disputed northern city of Kirkuk, on Thursday, then fled the scene when it failed to detonate.

Nobody was harmed in that attack. Two U.S. soldiers were killed in separate grenade attacks elsewhere in the area on Thursday, although it was not known who was responsible for the incidents.

The Thursday attack by the teenager came days after a 15-year-old boy lobbed a grenade at another U.S.-Iraqi patrol in the same city. One vehicle was damaged and the boy was captured, the military said.

A boy between the ages of 14 to 16 threw a grenade at a joint convoy of U.S. soldiers and Iraqi police in Hawijah on May 26, but no injuries or damage were reported, according to the statement.

The military also said a boy as young as 14 was the driver in a suicide car bombing that killed five Iraqi policemen in Kirkuk on May 12.

Also in the oil-rich city, 19-year-old man was arrested by Iraqi police while trying to detonate a suicide vest at a Shiite mosque on May 1, the statement said.

The militant groups are trying to take advantage of the fact "that children do not draw as much attention and soldiers do not want to harm them," U.S. officers said.

Four alleged members of a group known to recruit children were arrested on April 14, the military said.

Children that are hurt while carrying out insurgent activities are also being used in insurgent propaganda campaigns, the military said.

The United Nations also has expressed concern that rising numbers of Iraqi youths have been recruited into militias and insurgent groups, including some serving as suicide bombers. It called them "silent victims of the continued violence." There have also been several recent suicide bombings by women.

The U.S. military released several videos last year seized from suspected Al Qaeda in Iraq hideouts that showed militants training children who appeared as young as 10 to kidnap and kill. Children have also been used as decoys in Iraq.