President of the National Assembly and self-declared interim president of Venezuela Juan Guaidó speaking at a town meeting in Caracas. Photo by Molina86/Shutterstock.com

Venezuela's U.S.-backed opposition came under increasing scrutiny for a case in which two activists allegedly misappropriated funds designated to help Venezuelan security forces who deserted and crossed into Colombia.

Opposition leader Juan Guaidó said his diplomatic representative in Colombia will provide Colombian investigators with information about an opposition probe of the case. Guaidó, who is trying to topple Venezuelan President Nicolás Maduro, says anyone found guilty of wrongdoing must be punished.

“Dictatorships cover up corruption,” Guaidó tweeted. “We don't.”

Still, the alleged theft was a blow to an opposition movement that frequently accuses Maduro and his associates of large-scale corruption, contributing to the economic and humanitarian crisis that Venezuela has endured for years.

Maduro was quick to highlight the alleged opposition theft, saying it shows Guaidó's camp cannot be trusted.

“Corruption isn't new in the opposition,” he said. “The evidence is coming out.”

Hundreds of Venezuelan security forces heeded an opposition call to leave their posts in February, around the time that Guaidó tried to deliver U.S.-provided aid from Colombia and Brazil into neighboring Venezuela. The attempt collapsed when Venezuelan forces loyal to Maduro blocked aid trucks and clashes broke out.

Many of the Venezuelan security forces who fled into Colombia ended up in limbo, staying in hotels and other lodgings with no means of supporting themselves. Working with Colombian authorities, the Venezuelan opposition set up a plan to provide food and shelter for deserters and any family members who had joined them.

Humberto Calderón Berti, the top opposition envoy in Colombia, has said he started an internal investigation into the alleged corruption two months ago after a tip from Colombian intelligence. He will present the results of the probe to the Colombian attorney general's office, according to Guaidó.

The two suspects in the case were removed from their jobs after the internal investigation started, according to the Venezuelan opposition. They are currently in Colombia.

Also Monday, Venezuelan authorities freed three anti-government figures, including Gilber Caro, a substitute member of the opposition-controlled National Assembly who was detained April 26.

The releases came ahead of a visit to Venezuela this week by U.N. High Commissioner for Human Rights Michelle Bachelet, whose office says she will meet Maduro and Guaidó, as well as “victims of human rights violations” and their relatives.

In January, Guaidó declared that he was the rightful leader of Venezuela and that Maduro's reelection last year was a sham. The United States led dozens of countries in recognizing Guaidó's claim, and imposed sanctions on Venezuela's already deteriorating oil industry.

Maduro has defied the pressure, maintaining the support of Venezuela's military leadership as well as allies Cuba and Russia.

Christopher Torchia reports for the Associated Press.