Updated

FBI agents executed search warrants Thursday morning at the headquarters of California solar firm Solyndra, which received a $535 million loan from the federal government before filing for bankruptcy last week, FoxNews.com confirms.

Agents executed the search warrants at the company's headquarters in Fremont as part of a joint operation by the Federal Bureau of Investigation, Department of Energy and the Office of Inspector General, FBI spokesman Peter Lee said.

Lee told FoxNews.com that "multiple search warrants" were executed but said he could not provide details on what prompted the investigation.

"Everything’s under seal," he said.

The investigation comes one week after the company laid off 1,100 workers and filed for bankruptcy. The solar-panel manufacturer is now being sued by workers who abruptly lost their jobs.

More On This...

    Solyndra LLC was once touted by President Obama as a beneficiary of his administration's economic policies.

    The company was held up as the model for government investment in green technology. In addition to the $535 million loan guarantee, it received visits from the president and other state and federal officials.

    "I appreciated the chance to tour your plant and to see the incredible, cutting-edge solar panels that you're manufacturing, but also the process that goes into the manufacturing of these solar panels," Obama said while visiting the firm in Fremont on May 26, 2010.

    "It is just a testament to American ingenuity and dynamism and the fact that we continue to have the best universities in the world, the best technology in the world, and most importantly the best workers in the world. And you guys all represent that," he said.

    Solyndra filed bankruptcy amid hard times in the nation's solar industry. The price for solar panels has tanked, in part because of heavy competition from Chinese companies, dropping by about 42 percent this year.

    In a blog posting, Energy Department spokesman Dan Leistikow said Solyndra was a once promising company that had increased sales revenue by 2,000 percent in the past three years. The $535 million loan guarantee was sought by both the Bush and Obama administrations, he said, and private investors also put more than $1 billion into Solyndra.

    Republicans have been looking into the Solyndra loan for months. The House Energy and Commerce Committee subpoenaed documents relating to the loan from the White House Office of Management and Budget.

    Last Friday, Rep. Pete Stark, D-Calif., reportedly called on the firm's chief executive officer to give compensation and benefits to all employees laid off. Stark claimed the lay-off may have violated provisions of the Worker Adjustment and Retraining Notification Act, according to the San Jose Mercury News.

    Solyndra spokesman Dave Miller told the newspaper that Thursday's search came unexpectedly and said the company is "fully cooperating" with the investigation.

    FoxNews.com's Cristina Corbin and the Associated Press contributed to this report.