Saturday's attacks are the latest examples of the growing chaos in Iraq, only weeks away from elections set for 30 January.
The US commander in Iraq, General John Abizaid, acknowledged that the country's home-grown forces are not yet up to the task of protecting the elections, making a planned US troop increase necessary.
More than 40 Iraqis have been killed in the past two days alone.
Meanwhile, the deadly campaign against US troops continues.
Two US soldiers were killed by roadside bombs in Baghdad and north of the capital on Saturday, while the US military announced the deaths of two more soldiers in car bombings on their post near the Jordanian border the day before.
"While the Iraqi troops are larger in number than they used to be, those forces have to be seasoned more, trained more. So it's necessary to bring more
General John Abizaid,
US commander in Iraq
With the country still so unstable and elections eight weeks away, the US military now plans to increase its troop strength from 138,000 to about 150,000 by mid-January - slightly more than during the 2003 invasion that toppled Saddam Hussein - in an attempt to keep order during the vote.
In candid remarks, General Abizaid admitted the troop increase was not what Washington had envisaged.
"It had been our hope that we would be able to have a combination of increases that mainly were Iraqi troop increases," Abizaid, head of US Central Command, said.
"And while the Iraqi troops are larger in number than they used to be, those forces have to be seasoned more, trained more. So, it's necessary to bring more American forces."
Speaking at a regional security conference in Bahrain, Abizaid declined to speculate on when the Iraqi forces would be ready or say how many they now number. But he said they were, "constantly improving".
Baghdad's Green Zone continues
to be a favoured bomb target
Officials had hoped that the recent US-led attack of Falluja would put Iraqi fighters on the defensive. But the latest assaults demonstrate that they are still highly capable of hitting back where they choose.
Saturday's car bombs in Baghdad went off nearly simultaneously at about 9.30am 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.
At least seven were killed and 59
wounded in the Baghdad attack
Adil Hasan, 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 coordinated assault on a police station west of Baghdad in which fighters killed 16 police, looted the station's armoury and freed dozens of prisoners.
In the northern city of Mosul, a car bomber blew up his vehicle alongside a bus carrying pro-government Kurdish militiamen, killing at least 17 and wounding 40, an official said.
But Saadi Ahmad Bira, head of the office of the Patriotic Union of Kurdistan party (PUK) in Mosul, told Aljazeera that seven were killed and three others wounded by a car bomber.
"We accused followers of the Baath party of carrying out the attack," he said.
The men were being brought in from the mainly Kurdish city of Arbil to Mosul, where US and Iraqi forces have been battling fighters who staged an uprising last month, attacking police stations and government offices.
In an eastern district of Baghdad, a roadside bomb killed a US soldier and wounded five others on Saturday, the military said. Another bomb near the town of Ghalabiya, about 10km west of Baquba, north of Baghdad, hit a truck in a US military convoy, killing a soldier and wounding another, Master Sergeant Robert Powell said.
With regard to Friday's car bombings of a US forward operating base near Iraq's border with Jordan, the US command said on Saturday two US soldiers died in the attack.
Iraqi police have suffered heavy
losses in the upsurge of violence
Iraq closed its Karama border crossing into Jordan until further notice, Jordanian officials said.
The deaths - along with those of two US soldiers killed in roadside bombs in Baghdad and Kirkuk on Friday - brought the number of US military members killed since the war began in March 2003 to at least 1269, according to an Associated Press count.
Also on Saturday, a hospital official said the bodies of nine slain men wearing Iraqi National Guard uniforms were found in northwestern Iraq. The bodies were found on Friday in Tal Afar.
There have been at least 75 bodies discovered in and around that town and Mosul, about 50km to the east, since 18 November.
In yet another incident, police in the northern city of Samarra came under attack on Saturday. Mortars were fired at a police station after midnight, wounding two officers. Two policemen were injured in another attack at about 10am (0700 GMT), according to police Major Saadun Ahmad Matrud.
In other developments the Black Watch battalion has pulled out of Camp Dogwood and returned to its base in Basra.
Speaking to Aljazeera, Husham Halawi, the spokesperson for the British forces in southern Iraq, said their deployment was for a limited term.
"From the beginning, we said that the mission of the Black Watch regiment would last for only 30 days," he said. The unit was sent to Camp Dogwood to support the US attack on Falluja.