LONDON — Britain's Serious Fraud Office opened an investigation into the British business operations of Bernard Madoff on Thursday, raising the prospect that the alleged Wall Street fraudster could face criminal charges here.

The fraud office, which is cooperating with its U.S. counterparts, said its investigation would focus on British victims and "any criminal offenses that might have been committed in the U.K."

Responding to criticisms that it has moved too slowly in the past against illegal activity in London's huge financial sector, the agency said the inquiry showed its "new, faster approach to tackling fraud."

"The public say they want us to take early action, and this is what we are doing," fraud office director Richard Alderman said in a statement. "We will work closely with other law enforcement agencies to discover the truth behind the collapse of these huge financial structures."

The fraud office said it would speak with ex-employees of Madoff's interests in Britain, and called on investors or other stakeholders to come forward.

Madoff, 70, was arrested Dec. 11 on securities fraud charges alleging he duped investors out of as much as $50 billion in a giant Ponzi scheme. The former Nasdaq chairman is under house arrest on $10 million bail in New York, and his assets have been frozen.

Thousands of investors lost money in the alleged scheme, including Hollywood celebrities, hedge funds, international banks and charities.

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A prominent French financier who had entrusted his fortune and his clients' money to Madoff was found dead on Dec. 23 at his New York office, an apparent suicide.

A few days after his arrest and dramatic confession, Madoff voluntarily showed up at a closed-door meeting with regulators and FBI agents and began detailing how he pulled off his alleged scheme, officials familiar with the case said Wednesday.

But he has since stopped answering questions, hampering the investigation and killing any incentive for authorities to give him a break on bail, said the officials, who spoke on condition of anonymity because the probe was at a sensitive stage.

The issue of whether he should be allowed to remain under house arrest in his $7 million Manhattan penthouse made headlines this week when prosecutors made a sudden appearance in court and accused Madoff of violating his bail conditions by mailing jewelry and watches worth more than $1 million to relatives and friends.

Madoff's lawyer, Ira Sorkin, has confirmed that his client is not cooperating beyond agreeing to a freeze on his assets. He has argued that mailing the personal items was a harmless mistake, and that his client shouldn't be punished for it.

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AP reporters Tom Hays and Larry Neumeister in New York contributed to this report.