It has become a deadly tactic for insurgents: detonate an explosive near a target, then set off another in the same area to kill or maim anyone - soldiers, police or bystanders, who arrives on the scene.

Two such double-bombing plots were carried out in Iraq. Late in the day, twin explosives detonated near a Shi'ite mosque in Baghdad. Officials are quoted as saying that many of those killed or wounded were local civilians who rushed to the area after the initial blast.

Earlier, in Saddam Hussein's hometown of Tikrit, a double car bombing attack was carried out near the gates of a police academy.

Iraqi Police Major Qais Abdul-Qadir said, "A car bomb targeted policemen going to Jordan for a training course. There were casualties."

Authorities say six people were killed in the incident.

Meanwhile, U.S. military sources say a roadside bomb in east Baghdad killed an American soldier who was patrolling the area. It was the second roadside explosive to kill a U.S. serviceman in Iraq in these many days.

The U.S. military says four more suspects in last week's downing of a civilian helicopter north of Baghdad were arrested Sunday. Local residents provided information that led to those arrests and six others Saturday.

Insurgents released video of Thursday's attack, in which 11 non-military personnel, including six Americans, were killed.

Renewed insurgent activity in Iraq comes as the country struggles to form a new government. Nearly three months after historic elections, negotiations among major groups have yet to yield a Cabinet.

In a statement, outgoing Prime Minister Iyad Allawi said the task must be completed for the good of the country and to assure that Iraq continues on a democratic path.

Reports say discord continues between the main Shi'ite bloc closely tied to Grand Ayatollah Ali al-Sistani and Kurdish representatives seeking a more secular government amenable to local autonomy for Iraq's ethnic groups.

Iraq's transitional law dictates that Prime Minister-designate Ibrahim al-Jaafari would lose his post if no Cabinet is named by May 7.