HAVANA, July 30 (Reuters) - Cuba this week received shipments of food and medical supplies from allies Mexico, Russia and Bolivia in a bid to ease shortages and discontent amid the island"s worst economic crisis in decades and a surge in coronavirus cases. The donations, which authorities started distributing on Friday, come nearly three weeks after unprecedented protests broke out nationwide, spurred by frustrations with dire economic conditions and curbs on civil freedoms. Cuba blames the unrest on U.S.-backed mercenaries exploiting hardships it says were largely brought about by decades of U.S. sanctions and disguising attempts at unrest through the campaign #SOSCuba calling for humanitarian aid. Now it has taken back the humanitarian relief narrative, with the help of allies that have also blamed the U.S. trade embargo for much of Cuba"s woes. On Friday, a Mexican navy ship carrying 1,000 tonnes of beans as well as medical equipment and oxygen for COVID-19 patients arrived in the country, which currently has one of the highest infection rates per capita in the world. Two more will arrive shortly, Interior Commerce Minister Betsy Díaz said late on Friday on state television. "I want to personally thank President Andrés Manuel López Obrador who ... has ratified Mexico"s traditional rejection of the blockade and its will to help Cuba," Cuban Trade Minister Rodrigo Malmierca said at the ship-receiving ceremony. Pedro Monreal, author of a popular blog on Cuban economics, said the relief was "positive as an emergency measure" given the seriousness of the simultaneous health, economic and political crises. "This has a humanitarian and political angle," he said. "But when you look at the long term, its relative weight is low." Ricardo Torres, an economist with the Havana-based Center for the Study of the Cuban Economy, calculated, for example, that Vietnam"s promised donation of around 12,000 tonnes of rice would yield some 2 pounds per Cuban.