Two US soldiers were killed by roadside bombs yesterday, and two other Americans died in a suicide car bombing of their post near the Jordanian border the day before, the US military said.

The attacks came after a day of increased violence Friday, when attacks in Baghdad and the north killed 30 Iraqis -- most of them policemen -- and two more American troops.

The commander of US forces in Iraq acknowledged yesterday that US-trained Iraqi security forces, though increasing in number, are not yet up to the increasingly difficult task of keeping security during vital elections set for January 30.

In Baghdad, insurgents unleashed two suicide car bombs nearly simultaneously in the morning at a police station just across the street from a checkpoint leading into the heavily fortified Green Zone, the seat of American and Iraqi power in Baghdad.

Bursts of automatic fire followed the thunderous detonation, which shook windows several hundred yards away in buildings on the opposite side of the Tigris River.

Six policemen and another person were killed in the blast, and 59 people were wounded, hospital officials said.

Adel Hassan, a policeman who survived the attack with head injuries, said at a hospital crammed with victims that a "suicide car bomber sped into our place (the police station) ... and then there was an explosion."

In the northern city of Mosul, a suicide bomber pulled his explosive-laden vehicle alongside a bus bringing Kurdish fighters into the city. The attacker detonated the blast, killing seven militiamen from the Patriotic Union of Kurdistan, said Saadi Ahmed, a PUK official.

The militiamen were being brought in from the mainly Kurdish city of Irbil in order to protect PUK offices in Mosul. US and Iraqi forces have been battling insurgents who staged an uprising in the city last month, attacking police stations and offices of the Kurds, who are close US allies.

In fierce fighting in the city on Friday, gunmen tried to storm four police stations but were repelled, the US military said. About 70 guerrillas also ambush a US patrol with roadside bombs, rocket-propelled grenades and small-arms fire. After regrouping, US and Iraqi forces struck back on insurgent positions, killing more than two dozen fighters, the military said.

The latest attacks, however, were particularly audacious and sent a clear message that the insurgents can strike wherever they choose. The police station hit Saturday was just yards from the seat of American and Iraqi power in the country. On Friday, 11 carloads of gunmen attacked a police station, killing 16 policemen, on highway to Baghdad's international airport, which has been extremely dangerous despite frequent patrols by US troops.

Meanwhile, two American soldiers were killed Saturday by roadside bombs -- one in eastern Baghdad that wounded five other Americans, the other in the town of Ghalabiyah, 6 miles west of the insurgent hotbed of Baqouba, north of Baghdad, the military said. A suicide car bomb hit an American forward operating base near Iraq's border with Jordan on Friday, killing two US service members, the US command said Saturday. A Marine spokesman said the attack had been directed at members of the 1st Marine Expeditionary Force.

Iraq closed its Karameh border crossing into Jordan until further notice, Jordanian officials said yesterday.