More than 40 Iraqis have been killed in the last two days alone.
The insurgents' deadly campaign against American troops also continued. Two U.S. soldiers were killed by roadside bombs in Baghdad and north of the capital Saturday, and the military announced two other Americans died in a suicide car bombing of their post near the Jordanian border the day before.
Officials had hoped that the recent U.S.-led invasion of the insurgent hotbed of Fallujah would put Iraq's rebels on the defensive. But the latest attacks sent a clear message that insurgents are still highly capable of hitting back where they choose.
In other developments:
Saturday's car bombs in Baghdad went off nearly simultaneously at about 9:30 a.m. by a police station across the street from a checkpoint leading to the heavily fortified Green Zone, which houses the offices of Iraq's interim government and several foreign missions.
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.
Health officials said the bodies of seven people killed by the blast and 59 wounded were brought to two Baghdad hospitals. Officials said most of the victims were police officers, but the identities of all the dead were not yet known.
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."
The attack came a day after a highly coordinated assault on a police station west of Baghdad in which insurgents killed 16 police, looted the station's armory and freed dozens of prisoners.
Police in the northern city of Samarra also came under attack Saturday. Mortars were fired at a station after midnight, wounding two officers. Gunmen injured two policemen in another attack at about 10 a.m., according to police Maj. Sadoon Ahmed Matroud.
"We are moving toward the elections while the insurgents, terrorists and the former Baath regime members will try to destroy the security and they will try to build an environment that the people feel that there is no security," Iraqi Defense Ministry official Broska Noory Shausse said.
In the northern city of Mosul, a suicide bomber exploded his vehicle alongside a bus carrying pro-government Kurdish militiamen, killing at least seven and wounding three, an official said.
Along with Iraq's majority Shiites, Kurds back the upcoming elections, and the bombing may have been an attempt to drag them into a civil war.
The militiamen were being brought in from the mainly Kurdish city of Irbil to Mosul, where U.S. and Iraqi forces have been battling insurgents who staged an uprising last month, attacking police stations and government offices of the Kurds.
In fierce fighting in the city on Friday, gunmen tried to storm four police stations but were repelled, the U.S. military said. About 70 guerrillas also ambush a U.S. patrol with roadside bombs, rocket-propelled grenades and small-arms fire. After regrouping, U.S. and Iraqi forces struck back on insurgent positions, killing more than two dozen fighters, the military said.
In an eastern district of Baghdad, a roadside bomb killed an American soldier and wounded five others Saturday, the military said. Another bomb near the town of Ghalabiyah, 6 miles west of the insurgent hotbed of Baqouba, north of Baghdad, hit a truck in a U.S. military convoy, killing a soldier and wounding another, Master Sgt. Robert Powell said.
A suicide car bomb hit an American forward operating base near Iraq's border with Jordan on Friday, killing two U.S. service members, the U.S. 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 Saturday.
The killings - along with two Americans killed in roadside bombs in Baghdad and Kirkuk on Friday - brought the number of U.S. military members to have died since the war began in March 2003 to at least 1,269, according to an Associated Press count.