Nigeria’s anti-corruption agency has dropped a money-laundering case against a top cryptocurrency executive to allow him to get medical treatment abroad.

Tigran Gambaryan, a US citizen, was arrested on a business trip to Nigeria in February and later charged alongside his company Binance with laundering $35.4m (£28m) - which they denied.

The 40-year-old was in charge of financial crime compliance at Binance, the world's largest crypto exchange that Nigeria blames for much of its recent economic turmoil.

It accused the digital platform - where investors can buy, sell and trade cryptocurrencies - of fixing exchange rates and currency speculation leading to the free-fall of the local currency.

The charges against Binance, including tax evasion offences that it denies, were part of a clampdown by the Nigerian authorities on cryptocurrency firms in general over fears they were being used for money laundering and financing terrorism.

Mr Gambaryan’s family has been calling for his release over concerns about his health, saying conditions at the Kuje Correctional Centre - a prison in the capital, Abuja where he had been held since April - were exacerbating a back problem.

“The herniated disc in his back has worsened to the point where it might leave permanent damage and affect his ability to walk,” his wife Yuki said in August.

The High Court judge has twice denied him bail, saying he was a potential flight risk.

This followed the escape from custody of his colleague Nadeem Anjarwalla, a British-Kenyan dual national who was Binance’s Africa regional manager.

He was arrested alongside Mr Gambaryan in February but fled the country within weeks of the pair being put under house arrest - and is still wanted by the Nigerian authorities.

According to the Reuters news agency, Gambaryan’s trial was adjourned last Friday as he was not able to appear because of illness.

The Economic and Financial Crimes Commission (EFCC) then announced in court in Abuja on Wednesday that it was dropping the case against him.

"We have withdrawn the money laundering charges against Tigran Gambaryan to allow him to get medical treatment outside the country," Reuters quotes EFCC lawyer Ekele Ihenacho as saying.

The tax evasion charges filed against Binance by the Federal Inland Revenue Service will still be pursued in court.

Binance has also fallen foul of US laws. Last November its founder Changpeng Zhao resigned and in April was sentenced to four months in prison for allowing criminals to launder money on his platform.