A revolt at a prison in the Brazilian city of Rio de Janeiro has ended after eight hostages were released, authorities say - but the violence left four inmates dead.

The 24-hour confrontation began on Wednesday in an apparent battle between rival drug gangs inside the high security Bangu One prison.

Soldiers conducted a big operation to hunt down Beira-Mar last year

It escalated when four prison guards and four construction workers at the prison were taken hostage, and special police forces surrounded the prison.

Two hostages were freed late on Wednesday, and the others were allowed to go unarmed on Thursday after negotiations, police said.

Officials say one of Brazil's most notorious drug barons, Luiz Fernando da Costa, better known as Fernandinho Beira-Mar or "Seaside Freddy", is thought to have instigated the violence.

Members of his gang were reportedly armed with pistols and grenades, but police say they surrendered their weapons after the standoff ended.

Most wanted

Local reports say the dead are all prominent drug traffickers, and members of a rival gang.

The objective was not escape, but to unite the leadership of the drug traffickers, said the Rio de Janeiro State Security Chief, Roberto Aguiar.

"Anyone who opposed this was eliminated."

Beira-Mar was the country's most wanted criminal before his capture in the Colombian jungle last year.

He was alleged to have supplied Colombian rebels with weapons in return for cocaine which he sold in Brazil.

Earlier this year, Brazilian officials released tapes of wire-tapped telephone conversations in which Beira-Mar was allegedly negotiating the purchase of a stinger missile from inside the jail.

Prison uprisings are frequent in Brazil and usually blamed on poor living conditions and overcrowding, correspondents say.

However, conditions at the Bangu jail are said to be better.