The former head of Enron electricity trading has pleaded guilty to a charge of conspiracy to commit fraud for his part in manipulating California's energy market to drive up power prices.

Timothy Belden, who headed up Enron's energy-trading operations in Portland, Oregon, admitted to one charge of conspiracy to commit wire fraud in a plea agreement, the US Department of Justice said on Thursday.

The investigation seeks to uncover all inappropriate and criminal conduct... by Enron and Enron employees

Larry Thompson, Justice Department

Mr Belden is the third former Enron official to be prosecuted since the firm filed for bankruptcy last December after posting a $1bn (�664.5m) loss.

Andrew Fastow, who oversaw Enron's books, was arrested earlier this month on multiple charges of fraud, conspiracy to commit fraud and money laundering.

Mr Fastow' assistant, Michael Kopper, pleaded guilty in August to conspiracy charges following a plea agreement, which is believed to have led to Mr Fastow's arrest.

California power scheme

Mr Belden has agreed to cooperate with authorities as part of the deal he struck with the government.

US Deputy Attorney General Larry Thompson told reporters during a press briefing on Thursday that Mr Belden was a key player in Enron's bid to manipulate West Coast power prices.

Fastow aide Michael Kopper pleaded guilty in July

"The investigation seeks to uncover all inappropriate and criminal conduct that was involved by Enron and Enron employees," Mr Thompson said in announcing the plea deal.

Mr Belden entered his guilty plea in federal court in San Francisco.

His conviction is the first since an investigation into power manipulation in the Golden State drove electricity and natural-gas prices sky high during the state's energy crisis in 2000-01.

Mr Belden faces up to five years in prison plus fines of up to $250,000 (�161,000) and pay restitution of $2.1m (�1.4m), according to the plea deal.

"These charges answer the question that has long troubled California consumers: Whether the energy crisis was spurred in part by criminal activity," said US Attorney Kevin Ryan in a statement.

"The answer is a resounding yes."

He said those who "served their own selfish purposes" in manipulating power prices in California and other western states must be brought to justice.