Diplomats are calling for the release of Tigran Gambaryan, an employee of the crypto exchange who was arrested in February.

The U.S. government has urged Nigeria to release an employee of the giant cryptocurrency exchange Binance who was arrested there in February and has faced mounting medical problems in prison, according to two senior State Department officials.

The detention of Tigran Gambaryan, a former U.S. law enforcement officer, has become a significant factor in the diplomatic relationship between the United States and Nigeria, said the officials, who requested anonymity to discuss a diplomatic matter.

Secretary of State Antony J. Blinken raised the issue with his Nigerian counterpart in May, the officials said. Other U.S. diplomats, including the ambassador to Nigeria, have called for Mr. Gambaryan’s release in private conversations with Nigeria’s president, finance minister, attorney general and trade minister, according to the officials.

The U.S. diplomats have argued that Mr. Gambaryan, 40, should be freed on humanitarian grounds, after he suffered from malaria and problems stemming from a herniated disk, the officials said. His family has said he hasn’t received adequate medical treatment, causing his health to worsen rapidly.

Mr. Gambaryan traveled to Nigeria in February to hold meetings with local officials about Binance’s business dealings in the country. Nigerian authorities said Binance, the world’s largest cryptocurrency exchange, had harmed the nation’s economy by allowing users to transfer funds out of the local currency, the naira, causing it to collapse.

Nigerian prosecutors charged Mr. Gambaryan and Binance itself with tax evasion and money laundering. The tax charges against Mr. Gambaryan were dropped, but the others are still in place. Binance denied the claims and argued that Mr. Gambaryan was a midlevel employee who should not be held responsible for the company’s actions.

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