The Venezuelan government is investigating the opposition leader heading a campaign to hold a referendum on firing President Nicolas Maduro.

The Venezuelan government is investigating the opposition leader heading a campaign to hold a referendum on firing President Nicolas Maduro, officials said.

Henrique Capriles said Monday that the government was seeking revenge for his efforts to have Maduro terminated as president this year. His term ends in 2019.

"They know they've lost popular support, that they don't have the people on their side. That's why they have targeted me this way," the former governor and ex-presidential candidate told reporters.

The Comptroller's Office will investigate budget management in Miranda state - where Capriles was governor - in 2011, 2012, and 2013, state officials said in a statement.

"Inspect whatever you like," a defiant Capriles said. "I have nothing to be afraid of."

Maduro narrowly defeated Capriles during a presidential election in 2013.

But the socialist "revolution" championed by Maduro and his predecessor Hugo Chavez is under the mounting pressure of a grinding economic crisis mainly fuelled by low oil prices.

The opposition-controlled National Assembly is trying to eject Maduro from office with the referendum drive and a bill that would declare the president to have abandoned his duties.