Coronavirus-hit countries are asking Cuba for medical help. Why is the US opposed?

Doctors and nurses of Cuba's Henry Reeve International Medical Brigade pose with a portrait of Cuban late leader Fidel Castro before travelling to Italy, at the Central Unit of Medical Cooperation in Havana, on March 21, 2020.

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'