The US administration has turned to the African continent as another destination to deport migrants who it says are convicted criminals.

While dozens have been flown to countries in Central and South America, 12 men from countries including Mexico, Myanmar and Yemen were last month sent to Eswatini and South Sudan. One South Sudanese was also flown back home.

Other African countries are also reportedly being courted by the US to accept people, whose home countries will not take them back, according to the US authorities.

President Donald Trump's mass deportation pledge drew support during his campaign last year. But UN rights experts and human rights groups are alarmed by what has happened and argue that these removals to a nation that is not the migrant's place of origin – known as third countries - could violate international law.

Third-country deportations can be legal - but only under certain conditions.

"The whole concept of third-country removal has to be seen in light of the broader concept of asylum," says Prof Ray Brescia, from the Albany Law School in the US.

"There is a principle in international law - non-refoulement - which means you are not supposed to return someone to their home country if it's unsafe for them, so a third country could provide a safe option," he says.

This principle not only applies to the migrant's home country but also to any third country they might be sent to.

If that country is unsafe, deportation may violate international law - as when the UK's Supreme Court blocked the British government's plan to send asylum seekers to Rwanda in 2023.

Due process is also essential.

Migrants must have the chance to challenge deportation if the destination is dangerous, based on evidence from credible sources like UN reports or US State Department findings. Courts are expected to assess this risk carefully.

"The courts should examine what kind of legal status migrants will have, if they'll be detained, and what kind of housing is provided," says Dr Alice Edwards, the UN Special Rapporteur on Torture and other Cruel, Inhuman or Degrading Treatment or Punishment.

But many migrants struggle to access legal support in time.

"It takes significant effort and access to a lawyer who can act quickly," says Prof Brescia.

"That legal route may not be available to everyone."

"They certainly do in two respects," says Prof David Super, from Georgetown University Law Center.

"There's no evidence the US is giving people a chance to challenge their deportation, and they're not permitted to send people to countries where they might face oppression.

"South Sudan and Eswatini have serious questions about their human rights records," he tells the BBC.

When the migrants were first bound for South Sudan in May, a legal challenge was filed in a US district court after the flight had already taken off.

The judge ruled that the attempts to deport the men had violated his order that migrants must be allowed to challenge their removal to third countries.

The plane was rerouted to Djibouti, on the East African coast, where the men were reportedly held in a shipping container on a US military base while the case was heard.

The case was referred to the Supreme Court which allowed the deportations to proceed but did not specify whether South Sudan was deemed a safe place for the migrants.

"What we've seen in similar cases is that people are often denied legal help when they need it, and proceedings begin far too late," says Dr Edwards.

"In this case, they were already en route to a US military base and that's deeply problematic."

She adds that the courts must remain apolitical, especially when basic rights are at stake.

Prof Brescia warns that the Supreme Court's decision could set a dangerous precedent.

"There's real concern it will encourage the administration to move even faster, before individuals can access the courts at all," he says.

In addition to being denied due process, migrants are being sent to potentially unsafe countries - violating international law.

The US State Department currently advises against all travel to South Sudan, citing threats including crime, armed conflict and kidnapping. Earlier this year, the country, one of the poorest in the world, was said to be on the brink of a return to civil war.

"There are very real concerns about law and order in South Sudan - about violence, instability, and ongoing conflict," says Dr Edwards.

Those deported to South Sudan are reportedly being held in a detention facility in the capital, Juba, known for poor conditions, according to political activist, Agel Rich Machar.

The government has not confirmed their location or how long they will spend in detention.

In Eswatini, a small landlocked kingdom in southern Africa, officials say the migrants are in a correctional facility and will be repatriated with support from the International Organization of Migration (IOM).

The US State Department has said Eswatini's prisons face problems of overcrowding, poor ventilation, and deficiencies in dietary nutrition and health services.

"We don't foresee they will stay long enough to be integrated into society," Eswatini government spokesperson Thabile Mdluli told the BBC, without giving any indication of how long they would stay in the country, or whether they would serve the rest of their sentences first.

The US government says those who have been deported to Eswatini committed "barbaric" crimes including child rape, murder and sexual assault.

A backlash is growing in Eswatini.

The country's largest opposition party, the People's United Democratic Movement (Pudemo) says that the agreement between the two countries was "human trafficking disguised as a deportation deal".

Pro-democracy activist Lucky Lukhele says the country must not become "a dumping ground for criminals".

Even if international law has been violated, Prof Super says the US is unlikely to face consequences as it does not recognise many international courts.

"This appears to be about deterrence, sending a message that if you come to the US you'll be treated very, very harshly," he says.

Regardless of legality, third-country deportations often place vulnerable individuals in unfamiliar environments with little support or legal status, says Dr Edwards.

"It's a deeply flawed idea."

She stresses that the human rights community is not trying to block each and every deportation - only where people face human rights violations.

The details of the deportation deals remain largely secret.

Ms Mdluli tells the BBC that Eswatini's reasons for accepting the deportees "remains classified information for now".

However, both the Eswatini and South Sudan governments cited their strong ties with the US as a key motivation.

Prof Brescia suggests some countries may fear US retaliation if they refuse, such as stricter visa rules or higher tariffs.

In April, the US said it would revoke all visas issued to South Sudanese nationals after it would not accept a deported citizen.

It is not clear if that has changed, now that it has accepted deportees from the US.

Political activist Machar says South Sudan has also agreed to this deal as it wants the US to lift sanctions on Vice-President Benjamin Bol Mel.

The US government issued sanctions against Bol Mel in 2021 due to alleged corruption and renewed them this year.

However, other countries, like Nigeria, are pushing back.

"We have enough problems of our own," Nigerian Foreign Minister Yusuf Tuggar said in July, rejecting a request to take in Venezuelan detainees.

Dr Edwards notes that such deals often come with incentives.

"In past arrangements of third-country deportations, large sums of money, as well as military and security cooperation, were part of the package," she says.

In March, reports said the Trump administration would pay El Salvador $6m (£4.5m) to accept Venezuelan deportees.