The bus was carrying mostly women and children

Police said they believed the Mara Salvatrucha gang could be responsible for the killings on Thursday in the northern city of Chamalecon.

The bus was driving through a busy neighbourhood when it was surrounded by gunmen and sprayed with automatic fire.

President Ricardo Maduro called the massacre a "barbaric and cowardly act".

The shooting happened 200km (125 miles) north of the capital, Tegucigalpa.

Deputy Commissioner Wilmer Torres said the bus was forced to the side of the road at 1940 local time (0140 GMT) by cars that pulled up at its front and back.

The attackers got out of the cars and sprayed the bus with bullets from AK-47 rifles.

Mr Torres said 16 passengers died on board the bus and the others died after being taken to hospital in nearby San Pedro Sula city.

Local media reports said six of the dead were children, 16 were women and six were men.

Death penalty

Mr Torres said a member of the Mara Salvatrucha had been arrested in connection with the attack.

The gunmen left behind a note saying they represented a guerrilla group, the Cinchonero People's Liberation Movement, opposed to the reintroduction of the death penalty in Honduras.

However, the group in question has not been active since the 1980s and is thought to be defunct.

The attackers' note also challenged a number of leading politicians who have come out strongly against organised crime - particularly the president of Congress, Porfirio Lobo.

Mr Lobo, a potential candidate in next year's presidential election, has been a strong advocate of the death penalty for serious crimes.

Gang violence

The Mara Salvatrucha is one of a number of Los Angeles-style youth gangs that sprang up in the region after their members were deported from the US in the 1990s.

The founders of the gangs were typically Central American youngsters whose families had fled to the US to escape civil war.

After peace accords were signed, they were sent back to their countries and took the street-gang culture with them.

The Mara Salvatrucha now has an estimated 25,000 members in Honduras, neighbouring El Salvador and other Central American nations.

Members of the gang formed the majority of the 104 victims of a fire at San Pedro Sula prison in May.

President Maduro offered his sympathy to the families in a television and radio broadcast, and said he would be visiting them personally.

"What happened tonight is a barbaric and cowardly act," he said.

He said the attack was not a threat against him or his ministers, but "an attack against all Hondurans."

He said the police and military had joined forces to find the attackers, and a reward of $50,000 (£26,000) for information leading to their capture was being offered.

"I'm asking the country to have confidence in their government," he said.