HILLA, (AFP) — A suicide attacker blew up a bomb-filled car at a police station south of Baghdad, killing 21 policemen on Thursday, as Iraqi forces braced for Al-Qaeda revenge attacks after Osama bin Laden’s death.

The attack, which also wounded at least 75 policemen, was the worst in Iraq in more than a month, and pushed security chiefs to install new checkpoints, tighten access to key roads and restrict movement between provinces.

The bombing left a two-metre (six-foot) crater and badly damaged the police station in the centre of the mainly Shiite city of Hilla, capital of Babil province, in addition to several nearby houses and shops, just days after US special forces killed bin Laden in Pakistan.

“The suicide bomber took advantage of the police station’s guards changing shifts to attack,” said Haidar al-Zazour, head of the Babil provincial council security committee.

“He managed to drive through the main gate and blew up his vehicle four metres (12 feet) inside the station’s perimeter.”

The chief of Hilla’s main surgical hospital put the toll from Thursday’s suicide bombing at 21 dead and 75 wounded, all policemen. Of the wounded, 30 were in serious condition, the doctor said, speaking on condition of anonymity.

The death toll was confirmed by a list of the fatalities posted inside the hospital.

The explosion badly damaged the facade and several sections of the police station, which houses the emergency-response brigade, an AFP journalist said.

Babil provincial council chief Kadhim Majid al-Touman said that the car was packed with 150 kilogrammes (330 pounds) of explosives.

The attack mirrored a similar one in March, claimed by Al-Qaeda, when a suicide bomber drove an explosives-packed vehicle into an army barracks while guards were changing shifts, killing 11 soldiers.

The Hilla blast was the deadliest to hit Iraq since March 29, when a band of Al-Qaeda gunmen and suicide bombers managed to storm a provincial council building in the central city of Tikrit killing 58 people.

Thursday’s suicide bombing also comes nearly a year after four co-ordinated car bombs against factory workers in Hilla, 95 kilometres (60 miles) south of Baghdad, killed 50 people on May 10, 2010.

Mainly Shiite Hilla lies just beyond the edge of a confessionally mixed area south of the capital that earned the monicker Triangle of Death during the sectarian bloodshed that peaked in Iraq in 2006 and 2007.

Over the years it has been repeatedly bombed by Sunni insurgents loyal to bin Laden, whose death US President Barack Obama announced late on Sunday.

No group has yet claimed responsibility for Thursday’s attack in Hilla, but security forces nationwide began tightening security in the wake of the attack.

“We have strengthened security measures around all police stations and government facilities to prevent any revenge operations Al-Qaeda might carry out,” said Moqdad al-Mussawi, spokesman for police in Najaf province, which borders Babil.

“This is expected, especially after the killing of Osama bin Laden.”

Security chiefs in several other provinces, including Kirkuk, Maysan, Dhi Qar, Karbala, Muthanna, and Basra, also said they were tightening security.

In the northern town of Tuz Khurmatu, meanwhile, a bomb targeting a local security chief killed two of his bodyguards and wounded the security chief and five other guards, police Colonel Ali Khalaf al-Hamdani said.

And in central Baghdad, a roadside bomb killed a civilian and wounded three others, an interior ministry official said.

A magnetic “sticky bomb” attached to a car in the main northern city of Mosul killed one person, a police captain said.

Violence is down dramatically in Iraq from its peak, but attacks remain common. A total of 211 Iraqis were killed in violence in April, according to official figures.

Some 45,000 American soldiers remain stationed in Iraq, with all of them set to withdraw by the end of the year, under the terms of a bilateral pact.

But a series of US officials visited Baghdad last month to press Iraqi leaders to decide quickly on whether or not they wanted an extended American military presence beyond the year-end deadline.