A federal grand jury has subpoenaed records about California´s energy crisis from at least two power sellers that state regulators accuse of scheming to drive up prices.

Both North Carolina-based Duke Energy and Oklahoma-based Williams say they received subpoenas from federal prosecutors in San Francisco as part of a grand jury investigation.

Assistant U-S Attorney Matt Jacobs says he can´t comment.

A Duke spokesman says he doesn´t know the full extent of the request. He says the company will cooperate.

In a statement, Williams said it also would cooperate. A call to the company was not immediately returned. The generators have denied that they withheld energy.

A state Senate panel also has been probing the price spikes and energy shortages that led to rolling blackouts in 2001.