Four Guatemalan policemen arrested in connection with the murders of three politicians from El Salvador have been killed in jail, police say.
The four policemen had been held in the jail since Thursday
They were shot dead inside the maximum security Boqueron prison, east of Guatemala City.
A riot is reported at the jail, with several officers taken hostage.
The bodies of the three Salvadorean lawmakers and their driver were found in their burnt and bullet-ridden car near Guatemala City last Monday.
The four high-ranking policemen had been held in Boqueron prison since their arrest on Thursday.
"It is confirmed that the four bodies are them," police spokeswoman Maria Jose Fernandez said.
Photographs of their bullet-ridden bodies were distributed outside the jail.
The circumstances of the killings are still unclear.
Most of the jail's inmates are members of the Mara Salvatrucha gang and the shootings are reported to have taken place during a riot over conditions.
But it is unclear if the riot started before or after the killings.
Riot police have now gathered at the prison.
Some of the relatives of inmates said that guards had let in the attackers at visiting time.
Prison sources told Spanish news agency Efe that armed gunmen had threatened guards and then hunted for the policemen.
Guatemalan police said they suspected drug gangs were behind the killing of the policemen. One of the dead men was the head of an anti-organised crime squad.
The Mara Salvatrucha is heavily involved in drug trafficking.
The three politicians killed last week were members of El Salvador's governing Arena party and were deputies to the Central American Parliament.
One was the son of Arena's late founder, Roberto D'Aubuisson, who was accused of being behind the assassination of Archbishop Oscar Arnulfo Romero in 1980.
The politicians from El Salvador were killed on Monday
Drug links, political motives or a case of mistaken identity have all been put forward as an explanation for the politicians' murder.
El Salvador's Attorney General Felix Garrid Safie has said the killings were almost certainly linked to organised crime.
The president of Guatemala, Oscar Berger, apologised to El Salvador and ordered an investigation into corruption in his country's police force.