CARACAS, Venezuela (AP) — The administration of Venezuelan President Nicolás Maduro has arrested human rights activist Rocio San Miguel, the government confirmed Sunday.

Tarek William Saab, Venezuela’s attorney general, wrote in his social media accounts that San Miguel had been arrested on charges of conspiracy against Maduro, but did not offer any details of the supposed case against her.

San Miguel, 57, is a lawyer and rights activist who has specialized in studying Venezuela’s shadowy, often corrupt armed forces.

Saab claimed San Miguel had been linked to a plot to kill Maduro or other officials and attack the armed forces.

San Miguel was arrested Friday at an airport in Caracas, and rights activists say they do not know where she was taken.

“We do not know where she is now,” said Gonzalo Himob, a leader of the rights and civic group Foro Penal, which estimates the Maduro regime is holding 261 political prisoners.

In December, Saab ordered the arrest of a dozen opposition members, including former National Assembly leader Juan Guaidó and three campaign staffers of presidential candidate Maria Corina Machado.

In January, the U.S. government pulled back part of the sanctions relief it granted Venezuela last year after the South American country’s highest court blocked the presidential candidacy of an opposition leader.

The prospect of a free presidential election was dealt a heavy blow that month when the country’s highest court upheld a ban on the candidacy of María Corina Machado, a longtime government foe and winner of the primary held by the U.S.-backed opposition faction.

The Department of the Treasury gave companies transacting with Venezuela’s state-owned mining company until Feb. 13 to wind down operations. The department had allowed transactions with the mining company in October after President Nicolás Maduro’s government agreed to level the playing field ahead of this year’s presidential election.