A reward for information leading to the arrest of Ruja Ignatova, known as the Missing Cryptoqueen, has been increased by US authorities to $5m (£4m).

The Bulgarian-born German woman, 44, is wanted by the FBI for orchestrating a $4.5bn cryptocurrency scam called OneCoin.

She has been missing since 2017 when US officials signed an arrest warrant and investigators began closing in on her.

Three weeks ago, a BBC podcast and documentary revealed her links to the Bulgarian underworld and the suspected mafia boss involved in her disappearance and, allegedly, her possible murder.

However authorities continue to pursue Ms Ignatova.

In 2022, the FBI added her to its top 10 most wanted list, offering a $100,000 reward, later upped to $250,000.

On Wednesday, that amount increased again twenty-fold, under the US State Department’s Transnational Organised Crime Reward Program.

"We are offering a reward up to $5 million for information leading to the arrest and/or conviction of German national Ruja Ignatova, known as 'Cryptoqueen,' for her role in one of the largest global fraud schemes in history," said US State Department spokesman Matthew Miller.

She is currently the only woman targeted under the US programme.

An equivalent $5m reward is on offer for information about Daniel Kinahan, named as the head of one of Europe’s biggest drug cartels.

The same amount is on offer for information about Semion Mogilevich, alleged to be a Russia-based crime boss, and Yulan Adonay Archaga Carías, known as Porky, the highest-ranking member of the MS-13 criminal gang in Honduras.

German authorities have already charged Ruja Ignatova.

In Bulgaria, where OneCoin operated from its capital, Sofia, an official on Wednesday said that she would be charged in absentia.

Jamie Bartlett, whose BBC podcast brought global attention to her story, believes the reward increase is aimed at people possibly still protecting her.

"The FBI are now refocusing their efforts on the people around Dr Ruja, trying to tempt her close associates to get in touch.

"$100,000 wouldn’t persuade a junior member of a crime syndicate or a personal bodyguard to call the FBI’s hotline - it’s far too risky. But $5m just might.

"We will probably know within a few weeks if it’s worked."