Drive west from Doha’s glistening glass towers, past two World Cup stadiums still under construction and out into the desert, and you’ll eventually reach a small hospital surrounded only by sand and shrubs.

At its entrance hang two flags rippling in the scorching breeze: one of Qatar, the other of Cuba.

The hospital belongs to the Qatar government, but its entire medical staff – 475 doctors, nurses and technicians – is from the Caribbean island half a world away.

The Cuban hospital, as it is officially known, opened in 2012, boasting world class facilities and services. But there is one thing that is not up to international standards: the salaries the Cubans are paid.

The Cuban hospital is entirely staffed by doctors, nurses and technicians from Cuba. Photograph: Pete Pattisson

At just over $1,000 (£778) a month, they receive as little as 10% of what other foreign medical professionals can make working in government hospitals in Qatar.

The remainder of their earnings are pocketed by the Cuban government under a secret deal with the Qataris.

Neither the Qatari or Cuban authorities would reveal details of the agreement, but sources with knowledge of the hospital estimate Qatar pays Cuba between $5,000 and $10,000 a month for each medical professional.

Cuba has been sending doctors around the world since the early 1960s; there are currently an estimated 30,000 Cuban doctors and nurses working in 60 countries. Starting with missions to Algeria and Chile, the programme has grown into a global exercise in soft power driven by humanitarian, political and economic goals. Cuban medical teams are often at the forefront of disaster relief efforts in Latin America.

Leasing doctors to other countries is the main source of hard currency for Cuba’s cash-strapped economy, earning the government $6-8bn a year – far more than it makes from tourism.

In the past decade, partly prompted by declining revenue from its medical programme in Venezuela, Cuba has turned to new countries with no shortage of money: Qatar and Saudi Arabia.

Cuba is a totalitarian state with a pool of captive, low-paid workers easily exploited as exportable commodities María Werlau, Cuba Archive

In a similar arrangement with Brazil, the Cuban government was reportedly paid about $4,000 a month for each medic, of which the doctors received $1,000.

When the rightwing Jair Bolsonaro, an opponent of Cuba, took power in Brazil last year, thousands of Cuban doctors left the country, prompting fears that poor areas of Brazil would be left without sufficient medical care.

Cuba is not the only country that exports its citizens to earn foreign currency. North Korea has also sent workers to Qatar under a programme with some similarities.

Although doctors sign up voluntarily to take part in the missions, US-based critics of the Cuban government say the programme is exploitative.

“I have no doubt that they are subject to a form of compelled labour … Cuba is a totalitarian state with a guaranteed pool of captive low-paid workers easily exploited as exportable commodities,” says María Werlau, the director of Cuba Archive, a Miami-based thinktank opposed to the Cuban administration.

Werlau says Cuba’s medics are victims of wage theft, passport confiscation, heavy surveillance and forced family separation.

Amid deteriorating relations between the two countries, the US has recently increased criticism of the medical missions.

The Cuban medical professionals are paid far less than other foreign medics in Qatar, with most of their earnings pocketed by the Cuban government. Photograph: Pete Pattisson

In June, the State Department downgraded Cuba to the lowest tier of its Trafficking in Persons report, saying: “The [Cuban] government did not take action to address forced labour in the foreign medical missions programme, despite persistent allegations Cuban officials threatened and coerced some participants to remain in the programme.”

However, others argue the medical missions are highly-coveted opportunities in a country where doctors earn just $40 to $70 a month.

“I don’t believe that they are being exploited,” says John Kirk, professor of Spanish and Latin American studies at Dalhousie University in Canada. “They are earning significantly more than they would earn at home. They have been trained in a socialist system, have paid nothing for their medical training, and understand that the superior amount paid to the Cuban government is used to subsidise the healthcare system back in Cuba.”

The Guardian spoke to several medics at the Cuban hospital and some defended the system.

“I believe we should help everybody,” says one. “Based on that, yes it is fair, because I know that the other amount is used to support our health and education system … but if you think only of yourself, of course it’s not fair.”

But a medic who defected from the mission in Qatar says he “felt like a slave” on discovering that other doctors in the country were being paid more than him. “We were doing the same thing and earning far less than them.”

One reason doctors join the programme is that, even allowing for deductions made by their government, Qatar remains a lucrative and sought-after posting for Cuban healthcare professionals. With such paltry salaries at home, its attraction is obvious.

“Life in our country is very hard and the salary is very bad,” says one medic at the hospital. “Here we earn money for [Cuba] and for us too … One part for the country, and one part for each person.”

No one knows the exact amount the Cuban government is earning from their labour, and some seem not to care. “The education in Cuba is free. The government prepares us for many years and so the government needs to take something for this,” says one.

Others sound less convinced. “I earn about $1,100. It’s not the best, but its not bad.” Told that other foreign medical professionals earn far more in Qatar, he nods in agreement, “Yes, but not Cuban people.”

A Cuban doctor contemplates a map of the world. The country is renowned for its medical internationalism. Photograph: Ramón Espinosa/AP

The medics say their families are allowed to visit, but not stay – a policy critics claim is a deliberate strategy to deter defections. Anyone who abandons a medical mission is barred from returning to Cuba – and their family – for a minimum of eight years, unless they are willing to rejoin the national health system.

“They are using what they love the most to make them think twice before leaving. It’s cruel, it’s inhumane, it’s unconstitutional and against international law,” says Annarella O’Mahony, a member of No Somos Desertores (“We are not deserters”), a group that campaigns for the right of Cubans who have abandoned state contracts to return home.

Anyone attempting to leave faces another problem: on arrival in Qatar, Cubans say they have to hand over their passports, a practice that is illegal in Qatar.

Qatar recently announced reforms to its labour laws, which for the first time may allow workers to change jobs without their employer’s permission, but it is unclear whether the Cuban medics will be free to find more lucrative work elsewhere in Qatar’s healthcare system.

Up until 2017, Cuban medical professionals who wanted to leave could seek asylum in a US embassy under a programme introduced by President George Bush in 2006. The defector from the Cuban hospital, who left in this way, says he knows of 16 others who did the same, though he was driven less by conditions in Qatar and more by the opportunity for a new life in America.

Barack Obama withdrew the legislation just before he left office in 2017 as part of efforts to normalise relations with Cuba. “Now they are trapped again,” says the defector.

Despite being cut off from his family in Cuba, the defector says he has no regrets about leaving. “I tell my mother when I talk by phone that, despite all the difficulties and pain, I would do it again. I will never return to Cuba. There is no future there.”

A spokesperson for the Hamad Medical Corporation, the government body that manages healthcare in Qatar, including the Cuban Hospital said: “As with similar Cuban health programmes around the world, salaries of hospital staff are paid for by the Cuban government.”

The Guardian repeatedly approached the Cuban embassy in Qatar for comment, but received no response.