Caracas (AFP) - An outbreak of violence between rival groups of inmates at a prison in eastern Venezuela has left 12 dead and 11 injured, the government said Wednesday.

A spokesman for the ministry of penitentiary affairs, who gave the toll of dead and wounded, said nine of those killed died of gunshot wounds.

The deadly clashes erupted early Tuesday in the eastern city of Barcelona at the Jose Antonio Anzoategui prison, considered one of the country's most violent.

The prison had been undergoing reforms aimed in part at disarming inmates, but "there are still arms there and there are prisoners who rebelled," the ministry spokesman said.

"At this moment, an investigation is still underway, and this Wednesday those responsible will be brought before the courts."

He declined to detail what caused the fighting.

A prisoner rights group said a power struggle took place within the gang that has de facto control over the prison.

"It was like a coup d'etat" against the gang's boss, who was killed in the fighting, said Carlos Nieto of the group Window on Freedom.

"The group that wanted to seize power were inmates who had been transferred from the General Penitentiary of Venezuela," some 350 kilometers (220 miles) to the west, he said.

The Venezuelan Observatory of Prisons, a non-governmental monitoring group, said 14 inmates were killed at the prison last year.

Estimates of the country's prison population range from nearly 55,000 to 88,000, many of them in overcrowded jails awaiting prosecution. The government provides no official figures on inmate populations.

The prison system has an official capacity of around 35,000 inmates.