Suicide bombers killed 20 members of Iraq's fledgling security forces near a U.S. marine base west of Baghdad and at a checkpoint north of the capital on Saturday in a spate of guerrilla attacks across the country. The surge in violence underlined the scale of the task facing the U.S. military and Iraq's interim government, which have sworn to crush the guerrillas before elections in January. Hospital officials said 16 Iraqi police were killed and up to 40 people were wounded when a suicide bomber struck an Iraqi police post near the marine base. Another suicide bomber blew up his vehicle near a checkpoint manned by Iraqi National Guards in the village of Ishaqi, close to the town of Samarra, north of Baghdad, killing four guards. A policeman was killed by a roadside bomb in Samarra. There was no let up in violence elsewhere across the heartland of central Iraq that the interim government and Washington blame on Saddam Hussein supporters and foreign Islamic militants. Guerrillas killed two Turkish truckers and wounded two in an attack on a convoy near the northern city of Mosul, police said. In central Baghdad guerrillas fired two mortar rounds, killing two civilians and wounding one, witnesses said. Six U.S. soldiers were wounded when their armoured vehicle was hit by a bomb on a highway leading to Baghdad airport.