A jailed prominent opponent of Venezuela's socialist government has been transferred to one of the country's most violent prisons, his lawyer said Saturday.

Daniel Ceballos phoned his mother before dawn Saturday to say he had been moved to a prison in San Juan de los Morros, attorney Juan Carlos Gutierrez told The Associated Press. That jail holds some of Venezuela's toughest criminals and is considered one of the most dangerous of the country's prisons, which are among the most violent and overcrowded in Latin America.

Ceballos, who was removed as mayor of the western city of San Cristobal during anti-government protests last year, had been held in a military prison outside Caracas alongside other jailed leaders of Venezuela's opposition.

Gutierrez said neither he nor any relative of Ceballos had seen the judge's order required for any such move. The lawyer said that he and Patricia de Ceballos, the politician's wife and successor as mayor, would go to the prison a few hours south of Caracas to verify his client's well-being.

President Nicolas Maduro's government issued no comment and calls by the AP to the Prisons Ministry and tribunal overseeing the case were not answered.

The transfer comes less than a week after Ceballos from behind bars won a primary in San Cristobal to stand as the opposition alliance*s candidate in legislative elections expected later this year. Under Venezuelan law, a win in the general election could free Ceballos from jail because legislators receive immunity from prosecution during their terms.

Ceballos was arrested in March 2014 and quickly convicted on charges of disobeying authority for his refusal to remove barricades set up by demonstrators in San Cristobal. Although he completed that one-year sentence, he was ordered held in jail while awaiting trial on more serious charges tied to his support for anti-government protests in the city, which kicked off a nationwide wave of anti-government unrest.

Human Rights Watch expressed concern about the prison transfer, saying Ceballos will now be interned with individuals charged with murder and rape.

"Given the fact that he is under the custody of the Venezuelan government, we make the government of President Maduro responsible for the life and physical integrity of Ceballos and others arbitrarily detained in the country," Jose Miguel Vivanco, Americas director for Human Rights Watch, said in a statement.