Under fire from angry Republicans, US Energy Secretary Steven Chu denied Thursday that now bankrupt solar panel firm Solyndra leveraged political ties to President Barack Obama for a government loan.

"The final decisions on Solyndra were mine," Chu told a key committee of the Republican-held House of Representatives. "Over the course of Solyndras loan guarantee, I did not make any decision based on political considerations."

Republicans have contended over the course of a nine-month-old investigation that Obama's administration may have improperly influenced the US Energy Department's decision to give the firm a $535 million government loan guarantee.

And they have said that the firm, once hailed as a shining example of Obama's push to create green jobs and compete with rival China in a new energy economy, was instead a symbol of unwise federal handouts.

Republican Representative Cliff Stearns, chair of the panel before which Chu appeared, charged that Obama officials "put politics before the stewardship of the taxpayers' dollars."

The White House denies any wrongdoing, and Democrats have charged that the Republican-led investigation, launched in March, aims to embarrass the president and derail his efforts to boost clean-energy projects in the United States.

Representative Diana DeGette, the committee's top Democrat, labeled the investigation "a three-ring circus" and declared that Republicans had "focused on firing partisan broadsides at the Obama administration."

They have also charged that Republicans, some of them professed skeptics of the scientific consensus around global warming, aim to help traditional energy firms in the oil and coal sectors.

Republicans have linked administration efforts to help the firm to the fact that a charitable foundation run by George Kaiser, a generous contributor to Obama's 2008 presidential campaign, was a major investor in the firm.

California-based Solyndra filed for bankruptcy in September, closed its doors and laid off 1,000 workers, leaving taxpayers on the hook for the loan.

Chu sidestepped Republican Representative Fred Upton's demand for an official apology, denying any "incompetence" or "any influence of a political nature" in administering the loan, blaming a "very very bad tsunami" of economic woes for taking down the company.

But Upton pointed to internal Department of Energy documents he said showed staff raised "red flags" about the firm's financial strength, warnings that "reached the highest levels" of the White House only to be ignored.

"Officials were shrugging it off and calling it par for the course," the Republican said.

Chu and some Democrats defended the embattled loan guarantee program -- which faces an outside review ordered by Obama -- as a necessity if the United States is to compete with competitors like China and Europe.

"The Chinese are eating our lunch," said Democratic Representative John Dingell.

"They certainly want to dominate the market," agreed Chu, who underlined that "this is a worldwide competition."

"When it comes to the clean energy race, America faces a simple choice: compete or accept defeat. I believe we can and must compete," he said.