House investigators said they have uncovered evidence that White House officials became personally involved in an Energy Department review of a hot-button $535 million loan guarantee to the now-failed California solar company Solyndra.

The allegation surfaced in a letter House Energy Committee Chairman Fred Upton (R-Mich.) sent to the White House Thursday night, saying he planned to accelerate efforts to understand an investment deal that may have left taxpayers out half a billion dollars.

“We have learned from our investigation that White House officials monitored Solyndra’s application and communicated with [Department of Energy] and Office of Management and Budget officials during the course of their review,” the letter says.

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