Insurgents pressed their campaign to demolish the fledgling Iraqi security forces Sunday, killing 18 members of the Iraqi National Guard and a civilian with a suicide car bomb north of Baghdad, the U.S. Army said.

Insurgents also killed several police officers and local officials in other attacks around the country Sunday.

Scores of national guard and police officers have been killed in the past few weeks as insurgents have sought to cripple the interim government and disrupt national elections scheduled for Jan. 30.

The Army said elements of the 82nd Airborne Division had arrived in the beleaguered northern city of Mosul to reinforce troops there. Troops also have been bolstered in Baghdad in preparation for the elections. Total U.S. forces in Iraq are projected to rise this month to 150,000.

Also on Sunday, leaders of the country's most powerful political coalition, which is led by Shiite parties, conducted a surprise news conference in Baghdad. They urged Sunni Arabs to take part in the elections and sought to dispel fears that they were under the sway of Iran or were trying to establish an Islamic theocracy.

Leaders of the coalition, the United Iraqi Alliance, said elections must proceed despite the violence, which is concentrated in Sunni regions north and west of Baghdad.

The car bomb attack Sunday near Balad, site of a U.S. air base about 50 miles north of Baghdad, was one of the deadliest blasts in months and punctuated a week in which insurgents have aggressively attacked Iraqi security forces.

A four-wheel-drive vehicle crammed with explosives blew up next to a bus full of national guard officers, police said. In addition to the 19 people killed, six guardsmen were wounded.

The bombing came a day after the Iraqi affiliate of al-Qaeda, led by Jordanian militant Abu Musab al-Zarqawi, released a video showing five Iraqi guardsmen being executed. In a statement, the insurgents promised to "slaughter" Iraqis who serve in the national guard or the police.

Several other attacks on Iraqi security forces and officials were reported Sunday by domestic and foreign news agencies, usually based on police reports. Neither the interim Iraqi government nor the U.S. military issues a complete accounting of each day's violence.

In Samarra, also in the Sunni heartland north of Baghdad, three police officers were shot dead while on patrol, according to news reports, and a national guard officer was killed in Kirkuk. A deputy governor of Diyala province, in the same north-central region, also was killed.

In Basrah, in far southeastern Iraq, three police officers were shot to death in the center of the city, local hospital officials said.