MEXICO CITY, May 11 (Reuters) - Mexican President Andres Manuel Lopez Obrador said on Tuesday that U.S. Vice President Kamala Harris told his government the United States was willing to send AstraZeneca vaccines it was not using to other countries once they have been tested.

Millions of doses of AstraZeneca's COVID-19 vaccine manufactured at a U.S. plant that had a contamination issue that were previously shipped to Mexico were deemed safe and approved by two regulators, Mexico's deputy health minister said last month.

Lopez Obrador earlier this month said the United States would probably send his country 5 million more doses of the AstraZeneca vaccine, as the company acknowledged production in Latin American had suffered multiple setbacks.

Mexico is struggling with behind-schedule local AstraZeneca production and shortfalls in deliveries from foreign suppliers and has asked the United States to help with more vaccines.

The request is in addition to some 2.7 million AstraZeneca doses Washington sent to Mexico in March.

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Harris "told us they are very willing to deliver to countries that don't have vaccines what they've accumulated from the AstraZeneca vaccine," Lopez Obrador said at a regular news conference.

"But before making those shipments they are carrying out tests on the vaccines because they don't want to send something that's not in good condition, that they're not vaccines which have expired," he said.

The U.S. Food and Drug Administration halted production at the U.S. plant in Baltimore which had been manufacturing COVID-19 vaccines for AstraZeneca and for Johnson & Johnson while it investigated issues that led to millions of doses being ruined.

The AstraZeneca vaccine has not yet been authorized for use in the United States.

Lopez Obrador added that Pfizer Inc has started to send Mexico COVID-19 vaccine doses manufactured in the United States.

The U.S. government has been under mounting pressure to provide surplus vaccines to other nations desperately in need as it makes swift progress vaccinating its own residents and as U.S. demand declines.

Many countries where the virus is still rampant are struggling to acquire vaccine supplies to help tame the pandemic.

(Reporting by Anthony Esposito and Frank Jack Daniel; Editing by Bill Berkrot)