A former Guinea-Bissau navy chief convicted of drug trafficking in the United States is likely to be released from prison in early 2017 and returned to his country, US authorities said Wednesday.

Jose Americo "Bubo" Na Tchuto was sentenced Tuesday by Judge Richard Berman in a New York federal court to four years in prison, according to a spokeswoman for the federal prosecutor.

But because Na Tchuto has been imprisoned since April 2013, he has already served the bulk of his sentence and was expected to be released in April 2017, when he will be deported to Guinea-Bissau, the spokeswoman said.

If he returns to the United States, his sentence requires that he be placed "under supervision for five years," she added.

Na Tchuto, a US-designated international drug "kingpin," was captured off the West African coast by agents of the US Drug Enforcement Administration in April 2013.

Na Tchuto pleaded guilty to one count of conspiracy to import a controlled substance, which could entail a life sentence.

The conditions under which he pleaded guilty were not revealed, and the corresponding documents have been sealed.

His arrest, and the US indictment two weeks later of General Antonio Indjai, head of the Guinea-Bissau army, highlighted the rise in drug trafficking in West Africa, and the country's role as a transit point for the cocaine trade.

Guinea-Bissau has been plagued by military coups and instability since its independence from Portugal in 1974, and in recent years has become a cocaine-trafficking hub.