CARACAS (AFP) - At least 55 people were killed and 90 others wounded Saturday in clashes between prison gangs and security guards at a prison in northwest Venezuela, a hospital director said. Television images showed National Guard troops surrounding the Uribana prison in Lara state as inmates in bloody clothes were taken out of the building.  Behind the barriers, relatives of the prisoners - most of them women - waited for news of their loved ones, many of them in tears. Most of those injured had suffered gunshot wounds, said hospital official Ruy Medina. He called the death toll "alarming", saying it was based solely on bodies brought to the hospital.

Medina said the inmates began arriving at the hospital shortly before midday, and that 14 of the injured had wounds severe enough to require surgery.

Iris Varela, the minister responsible for Venezuela's prisons, said earlier Saturday that there were an "undetermined number" of casualties from the clashes. Attempts by AFP to get an update from the ministry later in the day were unsuccessful.

Vice President Nicolas Maduro, freshly back in the country after visiting recovering President Hugo Chavez in Cuba, called the riot "regrettable" and "tragic".

He announced a full-scale investigation into the clashes by the prosecutor's office.

Varela said the riot was sparked after inmates rebelled when prison authorities launched a sweep of the facility in search of illicit weapons.

Authorities had swept to "completely disarm" the prisoners after receiving a tip-off that prison gangs were readying to fight, she said.

Opposition parties immediately attacked the government, accusing it of exercising lax control over the prison system.

"Who will they blame for this massacre this time around?" opposition leader and former presidential candidate Henriques Capriles said in a tweet.

"The government is incapable and irresponsible," he added.