Guerrillas killed 20 people in attacks in Iraq Tuesday, and Prime Minister Iyad Allawi acknowledged what he called pockets of the country would be too unsafe for voting in a Jan. 30 election.A suicide car bomber killed seven policemen in Tikrit, Saddam Hussein's home town and a Sunni Muslim stronghold in northern Iraq, and gunmen shot dead eight people in a minibus south of Baghdad.
A group led by al Qaeda ally Abu Musab al-Zarqawi said it carried out the bombing against what it called "cowardly mercenaries" at police headquarters in Tikrit. Eight police officers were also wounded.
Repeated guerrilla attacks on Iraqi police and soldiers, who will be tasked with protecting polling stations, have deepened fears of major bloodletting on the day Iraqis vote for a 275-seat national assembly.
All 13 members of a committee organizing the election in Iraq's restive Anbar province, scene of numerous insurgent attacks, resigned after receiving death threats, the head of the team said.
President Bush spoke to Allawi by telephone about preparations for the election and both men agreed it should go ahead as planned, U.S. officials said.
"Both leaders reiterated the importance of moving forward on the date set by the Independent Iraqi Election Commission of Jan. 30," said White House spokesman Scott McClellan.
The attack on the minibus, in an area known as the "Triangle of Death," occurred shortly after the Tikrit blast. Gunmen kidnapped three people from the vehicle after killing all of the others inside, police said.
It was not immediately clear who had been targeted. Sunni insurgents regularly strike at Iraqi security forces and Shi'ite pilgrims in the lawless zone of dusty towns.
In the volatile northern city of Samarra, a roadside bomb triggered against a joint U.S.-Iraqi convoy killed two Iraqi National Guards, police said. A second bomb killed a policeman and a third killed two more National Guards.
Leading Sunni Arab parties say they will boycott the poll because violence in the Sunni heartland will scare away voters and skew results to favor Iraq's majority Shi'ites, who expect to emerge dominant after years of oppression under Saddam.
Insurgents have stepped up attacks, killing more than 100 Iraqis in the past week alone, mostly security force members they regard as collaborators with Washington.
A senior U.S. commander said last week four of Iraq's 18 provinces, including parts of the capital, were still too insecure to hold elections and predicted a surge of violence.
Monday, gunmen assassinated Baghdad's deputy police chief, and a suicide bomber in an explosives-packed vehicle resembling those used by police rammed a police compound in southern Baghdad, killing at least three people.
The shooting of Brigadier Amer Nayef occurred just six days after guerrillas assassinated Baghdad's provincial governor.
Allawi said Iraq would spend heavily to boost and train its fledgling security forces this year to try to crush guerrillas.
In a presentation to Iraqi army and police officers and reporters, Allawi said the New Iraqi Army -- which has been merged with the National Guard -- would be increased to a force of 150,000 from 100,000.
More training and equipment would be provided for the police, he said.
Monday, Britain pledged another 400 troops for Iraq to help shore up security for the election. Defense Secretary Geoff Hoon said Britain would deploy a battalion of the Royal Highland Fusiliers "for a limited period of time."
U.S. troop numbers have already been raised to their highest level since the U.S.-led invasion of Iraq in March 2003.