A $5m (£4m) reward is being offered in the hunt for the fugitive "Cryptoqueen" Ruja Ignatova.
Bulgarian-born Ignatova, who has German citizenship, has been on the FBI's most-wanted list since 2022 for fraud and money laundering.
The 43-year-old is accused of defrauding investors out of $4bn (£3.3bn) by selling a fake cryptocurrency called OneCoin, founded in Sofia in 2014.
The US agency, which has called OneCoin "one of the largest global fraud schemes in history", previously offered a $100,000 (£82,463) reward for her capture.
However, that has now been raised to £4m.
"Ignatova is believed to travel with armed guards and/or associates. Ignatova may have had plastic surgery or otherwise altered her appearance," states her FBI wanted poster.
Meanwhile, Bulgaria's chief prosecutor said on Wednesday he would press charges against Ignatova, who disappeared in late 2017.
"She will also be charged in absentia in our country, which will allow the start of a procedure for the confiscation of her illegally acquired property," he said.
The FBI believes she could be using a German passport to travel to countries such as the UAE, Russia, Greece and Eastern Europe.
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Ignatova's last known movements were taking a Ryanair flight from Sofia to Athens on 25 October 2017.
She fled after bugging a flat belonging to her American boyfriend and learning he was cooperating with the FBI, according to prosecutors.
When it added her to the most-wanted list, the FBI said it believed she escaped with a "tremendous amount of cash" - enough to "buy a lot of friends".
There has also been speculation she may have been murdered on the orders of the 'Godfather' of the Bulgarian mafia.
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OneCoin co-founder Karl Sebastian Greenwood was sentenced to 20 years in US prison last year and ordered to pay back $300m (£237m).
The fake cryptocurrency raked in huge amounts using a pyramid scheme model that offered commissions for members to entice others to get involved.
