Venezuelan authorities say they’ve arrested two top former officials in a widening corruption probe into the state-run oil industry.

The nation’s chief prosecutor says that Eulogio del Pino and Nestor Martinez were arrested Thursday.

Del Pino was serving as oil minister and Martinez as president of state-run PDVSA until both were removed Sunday by President Nicolas Maduro in a cabinet shakeup.

It follows the recent arrests of six executives of PDVSA’s Houston-based subsidiary Citgo, five of whom hold American passports. There also reports that Del Pino’s predecessor and one-time mentor Rafael Ramirez has been removed as Venezuela’s ambassador to the United Nations.

Venezuela has the world’s largest oil reserves.