BAGHDAD — At least 18 people were killed in clashes between al-Qaida fighters and former insurgents who turned against the terror network, Iraqi police and a former insurgent leader said Saturday.

Most members of the Islamic Army, a major Sunni Arab insurgent group that includes former members of Saddam Hussein's Baath Party, joined U.S. forces battling al-Qaida in Iraq earlier this year, though some of the group's leaders deny any contact with American troops.

A top Islamic Army leader, known as Abu Ibrahim, told The Associated Press that his fighters ambushed al-Qaida members near Samarra on Friday, killing 18 people and seizing 16 prisoners.

An Iraqi police officer in the area corroborated Abu Ibrahim's account, and said the hostages would not be transferred to Iraqi police. Instead, he said he believed the Islamic Army would offer a prisoner swap for some of its members held by al-Qaida. The officer spoke on condition of anonymity because of the situation's sensitivity.

"We found out that al-Qaida intended to attack us, so we ambushed them at 3 p.m. on Friday," Abu Ibrahim said. "We have killed 18 people, including some Arab foreigners, and we have detained 16 others. We also seized weapons and eight vehicles," he said.

Abu Ibrahim would not say how many, if any, Islamic Army members were killed.

The clashes raged for nearly four hours Friday about 9 miles southeast of Samarra, the insurgent commander said. Police said they knew about the battle, but were unable to reach the site because it was too violent. It is an area known to have a heavy al-Qaida in Iraq presence.

Abu Ibrahim contacted Iraqi police in Samarra and told them his plans to attack al-Qaida, according to the officer and Abu Ibrahim himself.

He asked that Iraqi authorities inform the American military about his plans, and requested that no U.S. troops interfere, they said. He worried that U.S. helicopters might mistakenly fire on his fighters, rather than on the al-Qaida members, since they had no uniforms and were indistinguishable from the militants, they said.

The U.S. military had no immediate comment on the matter.

Meanwhile, roadside bombs killed at least seven Iraqis early Saturday, police said, and the American military issued a statement saying a U.S. soldier was killed in Diyala province.

The soldier, assigned to Multi-National Division-North, died from injuries suffered in an explosion on Friday, the statement said. Three more soldiers were wounded in the blast, and evacuated to a U.S. combat hospital, it said.

At least 3,861 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an AP count. The figure includes eight civilians working for the military.

Saturday's Iraqi death toll included four civilians who died on minibuses hit by roadside bombs on their way to work, police said.