El DORADO, Venezuela (AP) _ Rival factions clashed inside Venezuela's notorious El Dorado prison Thursday, leaving at least 29 prisoners dead. Some victims were beheaded, a local official said. Thirteen inmates were seriously injured.

Details about the riot were sketchy because the prison, located in a remote area of the Amazon jungle near the country's southern border with Brazil, lacks telephone service.

Initial reports put the death toll at 42, but by late Thursday, the Justice Ministry had reduced the estimate to 29.

``The dead inmates are mostly Guajiro (Indians), 12 of whom were killed by knife and then burned,'' the ministry said in a one-page statement faxed to news agencies. ``Two of them were decapitated.''

Carlos Chancerol, mayor of the nearby town of Tumeremo, told the cable television station Guayana that inmates kicked the heads of decapitated prisoners along cell block hallways before the National Guard restored order.

The thirteen injured inmates were treated for multiple stab and gunshot wounds, said Rafael Rojas, a doctor at the nearby Tumeremo clinic.

The prison violence at El Dorado, located 450 miles southeast of the capital Caracas, was the deadliest in the South American nation since Jan. 1994, when 109 inmates died in a riot and fire at Sabaneta penitentiary in Maracaibo.

The focus of Thursday's fighting was between El Dorado's longtime inmates and members of a gang who were transferred to the prison from Sabaneta in November.

The Justice Ministry said the violence began at dawn Thursday and order was reestablished by 8 a.m. Rojas said prisoners told him the rioting broke out at 2 a.m.

In a telephone interview with The Associated Press, Rojas blamed the riot on tensions created by the prisoner transfer in November.

Venezuela's prison system is among the most overcrowded, understaffed and violent in the hemisphere, according to Amnesty International and Human Rights Watch.

The system's 32 jails hold about 25,000 inmates, or nearly twice as many as they were built to house. Only about one in four prisoners was convicted in court. The rest await trial.

At least 208 inmates died violently last year, or four a week, according to the Justice Ministry. Drug abuse and rape are common.

Prison guards are undertrained and frequently abusive. Last October, guards at a jail in Caracas set off a fire in a cell, killing 25 inmates, according Antonio Marval, the Venezuela's former prison director.

Overcrowding was apparently not a problem at El Dorado. The Justice Ministry said it was built to hold 1,360 prisoners and there were only 380 there at the time of the riot.