The United States and Britain vowed Tuesday to help find and recover billions of dollars thought to have been stolen by the administration of ousted Ukrainian President Viktor Yanukovych.

U.S. Attorney General Eric Holder, speaking at an international asset recovery conference, told reporters in London that those responsible for the alleged theft will be held accountable and the recovered assets will be returned to the Ukrainian people.

Britain's Serious Fraud Office announced Monday the start of a money laundering probe, and said it has frozen $23 million in assets inside Britain. Authorities did not identify suspects or their nationalities.

Additionally, Swiss authorities in late February froze the assets of both Mr. Yanukovych and his son, along with 18 other former Ukrainian ministers and officials.

The Russian-leaning Yanukovych government was ousted in February after months of anti-government protests. It had long been the target of critics who have alleged rampant corruption and graft in that Kyiv administration.

Analysts have placed the value of the alleged Yanukovych graft as high as $20 billion. They say asset recovery could be complicated if stolen funds were stashed in countries beyond Western Europe or the United States -- largely because cooperation from other countries is not guaranteed.