Havana(CNN) Cuba is offering to send doctors to more countries struggling with the coronavirus. But don't accept their help, the US State Department says.

As health care systems around the world are strained to the point of collapse, Cuban health care "brigades" have been invited to assist medical workers in Italy, Venezuela, Nicaragua, Suriname, Jamaica and Grenada. On Tuesday, Cuban officials released video of a field hospital its health care workers had built in Lombardy, Italy, one of the regions hit hardest by the coronavirus.

But the State Department wants countries to reconsider asking Cuba for help in fighting the coronavirus pandemic. "Cuba offers its international medical missions to those afflicted with #COVIDー19 only to make up the money it lost when countries stopped participating in the abusive program," tweeted an account for the US State Department Bureau of Democracy, Human Rights and Labor on Wednesday.

"Host countries seeking Cuba's help for #COVIDー19 should scrutinize agreements and end labor abuses," the message said.

Recent requests for help by other countries have marked an abrupt turnaround. Cuba saw hundreds of doctors sent home from medical missions in Brazil, Ecuador and Bolivia in recent years, after the US criticized Cuba's medical assistance programs, accusing them of exploiting health care workers and spreading propaganda. The State Department did not immediately respond to a request for comment.

Cuba offers some countries free medical assistance out of solidarity, while other countries pay for the services. The workers who deploy typically receive only about 20% of the salaries the host countries pay for their assistance -- a reduced wage, but much more than Cuban doctors earn in hospitals back home, where a top salary is about $60 a month.

The Cuban government has said it keeps the majority of the overseas salaries to finance the island's free health care system.

Extremely effective at disaster relief

Like many institutions in Cuba, the local health care system has seen better days. But the hyper centralization of the Cuban government, which has been so disastrous for the island's economy, makes Cuba extremely effective at disaster relief. And while health professionals on the island operate on a shoestring, the system is geared to preventing disease rather than waiting to treat it.

After the first cases of coronavirus were discovered in Cuba on March 11 in three Italian tourists visiting the colonial city of Trinidad, thousands of Cuban health workers, including medical students, were sent by the government to go door to door across the island to search of people suffering from respiratory illness that could be the coronavirus.

Soon all the government resources were focused on the pandemic. Currently, Cuba has 57 confirmed cases with 1,479 other people who are hospitalized and being monitored for symptoms of the coronavirus.

Earlier this month, the government also took the unusual step of offering help to a British cruise liner with at least five confirmed coronavirus cases aboard and dozens more people suffering from flu-like symptoms. Several other islands including the Bahamas and Barbados, had already turned down the cruise ship.

The MS Braemar docked in the Port of Mariel, site of the boatlift of refugees fleeing the island to the US in 1980, and Cuban health workers carried out the risky, daylong operation of transporting more than 600 cruise ship passengers from the port to the runaway at Havana's airport, where four charter planes to England were waiting.

"I am very grateful to the Cuban government for allowing this operation to move forward," said Antony Stokes, the UK's ambassador to Cuba, on the day the Braemar arrived.

Now, as other countries' health care systems falter, more Cuban doctors are likely to be on the front lines of the pandemic. Those efforts should make the US government reconsider the nearly 60-year-old trade embargo on Cuba, said Mark Weisbrot, co-director of the Center for Economic and Policy Research, which recently called on the Trump administration to lift economic sanctions on Cuba, Iran and Venezuela as part of the fight against coronavirus.

"The sanctions have a more generalized and deadly direct effect by contributing to a more generalized scarcity of life-saving medicine and equipment because they exacerbate an economic downturn," Weisbrot wrote to CNN in an email. "This means more scarcities of vital medical needs and supplies, and more deaths."

If Trump did offer Cuba any sanctions relief, it would fly in the face of his policy of dismantling the Obama administration's opening to Cuba. Trump has also made clear he believes a tough on Cuba posture wins votes with Florida's conservative Cuban American community.

Last week, Trump offered an olive branch to a communist adversary, saying he would be willing to send aid to help North Korea fight the coronavirus. Despite Cuba's growing contributions to the battle against the pandemic, Havana is unlikely to receive a similar offer.