Baghdad: A wave of attacks killed 50 people in more than a dozen Iraqi cities, 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 (local time), 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."