Venezuela’s government arrested two high-level energy officials on Sunday following the detention of a former oil minister amid an investigation into billions of lost Petroleos de Venezuela SA revenue, according to Bloomberg.

Vice minister for oil Erick Pérez and vice minister for gas Juan Santana were arrested on Saturday, according to a person with direct knowledge of the situation but who requested anonymity because the information has not been made public. The arrests follow the detention of Maduro’s former oil minister Tareck El Aissami on Tuesday, a year after his resignation. 

El Aissami has been charged with treason and money laundering in connection with an alleged scheme in which billions of dollars in oil proceeds disappeared.

The country’s oil ministry did not immediately respond to a request for comment on the detentions.

The arrests come just months before the presidential election set for July 28, which has been highly criticized by the international community for unfair conditions and the shunning of candidate Maria Corina Machado, the winner of the opposition primaries in October. 

Nicolas Maduro, running for a third consecutive term, proposed on Saturday a constitutional reform to allow life sentences and political bans against anyone found guilty of graft, treason, and crimes “against the people.” As he campaigns on anti-corruption promises, the Venezuelan constitution’s maximum penalty is 30 years in prison. 

Former finance minister Simon Zerpa and businessman Samark López were also arrested on treason, appropriation and money laundering charges. More than 50 people have been detained so far, including judges, elected officials, business people and the head of the crypto oversight agency.

The US has said it’s willing to let an important oil and gas license expire on April 18 if the socialist government doesn’t take steps toward democratic elections.