At least 12 people have been killed in a gun battle between police and suspected drug traffickers in the Brazilian city of Rio de Janeiro, authorities say.

A policeman died in the shooting in a slum of the city, the Secretary for Public Safety in Rio, Colonel Josias Quintal, said.

He said the shooting began when officers tried to arrest suspected drug traffickers.

More than 250 policemen took part in the operation.

It was not immediately clear if any one was arrested or if any drugs or arms were apprehended.

Correspondents say drug gangs, selling mostly cocaine and marijuana, control most of the shantytowns of Rio de Janeiro - a city which has one of the world's highest murder rates.

Transit route

The gunfight began at about 0800 local time (1000 GMT) after police entered the Rebu and Corea shantytowns, police spokesman Renato Homen said.

Eleven drug traffickers died in the battle, he said.

One policeman was in serious condition after being shot in the head, Mr Homen said. Two more were wounded, but their injuries were not believed to be life-threatening.

Two people were arrested last November in the Brazilian capital, Brasilia, suspected of using a hearse to smuggle drugs.

The two - a man and a woman - were discovered unloading 88 kilograms of marijuana from a secret compartment located under the coffin in the vehicle.

A study published in Brazil last year concluded that more young people below the age of 18 were killed by guns each year in Rio de Janeiro than in many areas of the world formally at war.

The study concluded that there were strong similarities between children involved in drug wars in Rio's slums and child soldiers elsewhere in the world.

Brazil is said to have become an important transit point for cocaine shipments from Bolivia, Peru and Colombia on route towards Europe and Africa.