An executive of the cryptocurrency firm Binance has escaped from custody in Nigeria, the authorities there say.
Nadeem Anjarwalla, a British-Kenyan dual national, was arrested in February with his US colleague Tigran Gambaryan.
Their detention came as the Nigerian authorities investigated alleged wrongdoing by Binance.
Nigeria said that Mr Anjarwalla fled the country with a "smuggled passport", but a family source has said he had left by "by lawful means".
The country is now "working with Interpol for an international arrest warrant on the suspect", the Office of the National Security Adviser (ONSA) said in a statement.
Binance has not commented on the accusations it has been facing.
"We were made aware that Nadeem is no longer in Nigerian custody. Our primary focus remains on the safety of our employees and we are working collaboratively with Nigerian authorities to quickly resolve this issue," a Binance spokesperson said.
Mr Anjarwalla, the company's Africa regional manager, and Mr Gambaryan, in charge of financial crime compliance at the firm, were arrested on 26 February after attending meetings in Nigeria's capital, Abuja, to which they had been invited by the government.
The authorities reportedly demanded that they name Nigerians trading on their platform.
A court granted the Economic and Financial Crimes Commission's request to detain the two executives for 14 days, but their continued detention was not authorised by the court and they were being held "unlawfully", a source close to the families told the BBC.
They were due to appear again in court early next month.
"The personnel responsible for the custody of the suspect have been arrested, and a thorough investigation is ongoing to unravel the circumstances that led to his escape from lawful detention," the ONSA said.
Nigerian media are reporting that Mr Anjarwalla asked the guards at a guest house where he was being held to allow him to go to the mosque last Friday but never returned.
The authorities had reportedly confiscated his British passport but the whereabouts of his Kenyan passport were unknown.
Meanwhile, the Nigerian authorities have formally filed tax evasion charges against Binance at the High Court in Abuja, and named Mr Anjarwalla among the respondents.
The Federal Inland Revenue Service is accusing the cryptocurrency platform of non-payment of value added tax, company income tax, failure to file tax returns and complicity in aiding customers to evade taxes through its platform.
Binance has not made a statement on these charges.
Last month, the Nigerian authorities clamped down on cryptocurrency firms in general over allegations they were being used for money laundering and financing terrorism.
