A wave of attacks killed 50 people in more than a dozen Iraqi cities on Tuesday, the anniversary of the US-led invasion of the country and just days before Baghdad hosts a landmark Arab summit.

The violence, which left 255 people wounded, bore the hallmarks of Al-Qaeda, which typically tries to launch coordinated nationwide mass-casualty bombing campaigns.

No group immediately claimed responsibility, however.

The attacks were swiftly condemned internationally, with United Nations envoy Martin Kobler describing them as "atrocious", White House spokesman Jay Carney adding that the US "strongly condemn" the violence, and Britain's Middle East minister Alistair Burt slamming them as "cowardly."

Bombings and shootings rocked 18 towns and cities spanning the northern oil hub of Kirkuk and the Shiite shrine city of Karbala, south of Baghdad, from 7:00 am (0400 GMT), in Iraq's deadliest violence in more than two months.

"We lost everything," said Mohammed Sobheh, a policeman wounded in the Kirkuk attack. "Not one of my colleagues is alive; they were all killed."

"I will never forget their screams as long as I live."

In central Baghdad, a car bomb exploded in the car park opposite the foreign ministry, despite dramatically heightened security in the capital in preparation for the March 27-29 Arab League summit.

At least three people were killed and nine wounded, officials said, underscoring concerns over Iraq's ability to maintain security for the meeting.

Parliament speaker Osama al-Nujaifi condemned the "brutal criminal" attacks, and said they were part of efforts by Al-Qaeda to "derail the Arab summit, and keep Iraq feeling the effects of violence and destruction."

Following the attacks, the government declared a week of public holidays from March 25 to April 1.

Coupled with Kurdish New Year festival Nowruz on Wednesday and the weekly Muslim day of prayer on Friday, much of Iraq will be largely closed until after the summit.

Security forces have mooted the possibility of imposing a city-wide curfew on March 29, when Arab leaders are expected in Baghdad.

Tuesday's deadliest attacks were in Kirkuk and Karbala, where a total of 26 people died.

In ethnically mixed Kirkuk, a suicide bomber blew up a vehicle at a police building, killing 13 and wounding 60, according to Karim Wali, director of the city's hospital. The vast majority of casualties were police officers.

The explosion, which was followed minutes later by a smaller car bomb, also badly damaged dozens of police cars and nearby homes.

In Karbala, two roadside blasts at the entrance to the city killed 13 people and wounded 48, according to provincial health spokesman Jamal Mehdi.

Karbala police's Major Alaa Abbas gave the same casualty toll in the city, home to the shrines of revered Shiite leaders Imam Hussein and Imam Abbas.

Hours before the foreign ministry attack, a car bomb detonated by a suicide attacker in the centre of the capital killed five people and wounded 28, officials said.

An early-morning gun attack on a Baghdad church also left three police dead.

Bombs in Hilla, south of Baghdad, Ramadi, west of the capital, and Baquba, in central Iraq, killed five people and wounded 44, officials said.

A later roadside bombing in Ramadi targeting Anbar provincial Governor Qassim Mohammed Abed killed one person and wounded eight, but Abed was unhurt.

Police said separate gun and bomb attacks in Salaheddin province, north of the capital, killed six, including a city councillor, and wounded 16. Gunmen also killed a member of the Shabak minority in the main northern city of Mosul.

Bombings elsewhere in the country wounded 42 people, and security forces said they defused six more car bombs.

Tuesday's violence was Iraq's deadliest day since January 14, when 53 people were killed in a suicide bombing outside the southern port of Basra.

The attacks come on the ninth anniversary of the US-led invasion of Iraq, which ousted Saddam Hussein.

Next week's Arab summit is the first meeting of the 22-nation bloc to be held in the Iraqi capital since Saddam's 1990 invasion of Kuwait.

Officials insist Iraq's forces are capable of maintaining security for the summit, but admit they may need to effectively shut down Baghdad to do so.