(Adds Qaeda claim)

By Lamine Chikhi

ALGIERS, Jan 2 (Reuters) - A car rammed into a police station in Algeria on Wednesday and exploded, killing four policemen and injuring 20 people, state radio said.

Al Qaeda's north African wing said the Toyota laden with at least 500 kg (1100 lbs) of explosives was driven by one of its members, according to a recorded statement aired by Al Arabiya television.

The blast left a crater three metres (three yards) wide, wrecked the outside of the building and damaged nearby homes, shops and a cafe in the town of Naciria, about 120 km (75 miles) east of Algiers, witnesses said.

"This morning at 7 a.m. one of the lions of the al Qaeda Organisation in the Islamic Maghreb, martyrdom-seeker Abdullah, ... drove (his car) into the judicial police quarters," a man told the Arabic TV news station.

He identified himself as Salah Abou Mohammad, a spokesman for the group.

An earlier Interior Ministry statement did not specify whether it was a suicide car bomb.

"We heard the loud thump of the blast at 7.15 a.m. (0615 GMT)," said one resident, who did not want to be named.

"A Toyota car was used in the bombing which killed four policemen and injured 20 people," state radio said.

It was the first major attack in Algeria since a double bombing in the capital Algiers killed at least 37 people on Dec. 11, including 17 United Nations staff.

Maghreb Al Qaeda claimed responsibility for that attack, which hit U.N. offices and a court building, saying it had targeted "the slaves of America and France".

Algerian Islamist rebels aligned themselves with Al Qaeda last year and began copying its tactics by carrying out a string of high-profile urban suicide bombings.

The group was previously called the Salafist Group for Preaching and Combat and preferred to ambush government security forces from its main base in the Kabylie region east of Algiers. (Additional reporting by Hamid Ould Ahmed in Algiers and Inal Ersan in Dubai; Editing by Giles Elgood)

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