Baghdad, Iraq ? At least 20 people were killed in Iraq on Monday by car bombers, roadside bombs, assault rifle fire and an explosive rigged to a headless body, as insurgents appeared to intensify efforts to derail nationwide elections set for Jan. 30.

The day’s first car bomb exploded around 9:30 a.m. outside the headquarters of interim Prime Minister Ayad Allawi’s political party, the Iraqi National Accord, shortly before Allawi was to appear at a news conference detailing a slate of candidates. Allawi was not injured, but three police officers and the bomber were killed, according to a government spokesman.

The Ansar al-Sunna Army, the group that asserted responsibility for a Dec. 21 bombing inside a U.S. military base in Mosul, posted an Internet statement heralding “more good news. … Body pieces of the apostates were scattered everywhere, and their cars caught on fire. … Thanks and gratitude to God.”

A Saudi newspaper reported Monday that the Mosul bomber was a Saudi medical student whose father was informed of his death by the Ansar al-Sunna group. The attack killed 22 people, including 14 U.S. troops.

The Asharq Al-Awsat identified him as 20-year-old Ahmed Said Ahmed al-Ghamdi, citing unnamed friends of the man’s father. The al-Ghamdis are a large Saudi clan, three members of which were among the Sept. 11 hijackers.

Another car bomber killed himself and four Iraqi National Guardsmen at a checkpoint in Dijail, a town north of Baghdad not far from where 22 guardsmen aboard a shuttle bus were killed Sunday by a car bomb.

The third car bomb was detonated around 3 p.m. by a man who pretended his sport-utility vehicle had broken down near a gate to the Green Zone, the fortified area of Baghdad that houses Iraq’s interim government and the U.S. and British embassies. The man waited for a convoy of the large, late-model SUVs that are widely known to carry Western contractors, diplomats and security personnel, then exploded his vehicle.

In another graphic attack, insurgents booby-trapped the decapitated body of a civilian in the city of Tall Afar, west of Mosul. When Iraqi police investigated the corpse, it exploded, killing one officer and wounding two, the government said in a statement.

Six National Guardsmen were killed by a pair of roadside bombs in Tikrit, the home town of former President Saddam Hussein. In Baiji, an oil refining city in the Sunni Triangle, a police major and a captain were killed in a hail of gunfire from a white sedan, police said. And in Baqubah, another insurgent hot spot about 35 miles northeast of the capital, gunmen assassinated a city councilman from nearby Khalis.

Iraqi and American security forces inspect the site of an explosion at a checkpoint in western Baghdad, Iraq. A suicide bomber blew up an explosives-laden car near the prime minister's party headquarters on Monday, killing three, as insurgents pressed their campaign to disrupt national elections.