Senior executives from a solar-energy firm that went bankrupt after getting a half-billion-dollar government loan have refused to testify at a congressional hearing where one politician accused them of a "heist".

The House Energy and Commerce Committee opened its hearing on Friday into Solyndra, a solar-panel manufacturer whose failure has become an embarrassment for the Obama administration and the president's push for "green jobs".

Brian Harrison, Solyndra's president and chief executive, and William Stover, the chief financial officer, refused to testify at the hearing on the $535m loan, invoking their constitutional right against self-incrimination.

The committee chair, Representative Fred Upton, commented that "it appears that we have a great heist of over half a billion dollars and possibly even willing collaborators, maybe even co-conspirators, called the US government, who rushed out a $535mn loan to Solyndra".

The California-based firm, which was granted a loan in an effort to highlight a push for new jobs in the renewable energy sector, has been the target of a congressional probe since February.

It sought bankruptcy protection on August 31 and the FBI later raided its offices.

"Let me just warn you and the other folks involved in this taxpayer rip-off," Upton said. "We're not done. No we're not."

Henry Waxman, a Democrat, criticised the actions of his Republican colleagues at the hearing.

"So I just want to take this moment to assert the fact that I think it's unseemly and inappropriate for members to be asking questions that we know you will not answer," he said.