Venezuela's government is facing mounting criticisms from activists and the U.N. human rights office for its handling of overcrowded and violent prisons following a clash between inmates and troops that left at least 58 dead.

Rupert Colville, a spokesman for the U.N. High Commissioner for Human Rights, expressed concern about what he called "an alarming pattern of violence in Venezuelan prisons, which is a direct consequence of poor conditions." He made the remarks at a news conference in Geneva on Tuesday.

Vice President Nicolas Maduro defended the Venezuelan government's efforts and said the "first steps" are being taken to improve the country's prisons.

The government has said that 58 people were killed on Friday at Uribana prison in the city of Barquisimeto when armed inmates clashed with National Guard troops.