Mbabane, Eswatini - Eswatini confirmed for the first time Monday that it had received more than $5 million from the US to accept dozens of people expelled under Washington's aggressive mass deportation drive.

The tiny southern African kingdom has taken in 15 men since President Donald Trump's administration struck largely secretive deals with at least five African nations to accept migrants under a third-country deportation program fiercely criticized by rights groups.

A document revealed by Human Rights Watch in September and seen by AFP said Eswatini agreed to take 160 deported people in exchange for $5.1 million to "build its border and migration management capacity."

Questioned in parliament about the arrangement, Finance Minister Neal Rijkenberg confirmed the government had received the $5.1 million.

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"We were told it was for the US deportees after we enquired," he said, adding the ministry had been kept in the dark throughout the process.

The first group of five men arrived in July aboard a chartered US military plane, with a second group received in early October.

Washington branded some of them "depraved monsters" convicted of crimes including child rape and murder.

They are being held without charge in Eswatini's maximum-security Matsapha Correctional Centre, notorious for detaining political prisoners, according to their lawyers.

One of them, a 62-year-old Jamaican who had reportedly completed a murder sentence in the US, was sent back to Jamaica in September.

Lawyers and civil society groups in Eswatini have gone to court to challenge the legality of the detentions.

Rijkenberg told parliament the money received from the US was funneled into the account of Eswatini's disaster agency, NDMA.

However, "NDMA is not allowed to use money it has not been appropriated," he said, vowing to regularize the process.

It was not immediately clear who from Eswatini signed the deal with the US.

Formerly known as Swaziland, the country is the last absolute monarchy in Africa. It has been led by King Mswati III since 1986, and his government has been accused of human rights violations.