President Joe Biden’s administration is stockpiling tens of millions of doses of a vaccine for the coronavirus disease 2019 (Covid-19) whose authorization in the U.S. remains uncertain, frustrating US allies who say those doses should be used now to save lives overseas.

The standoff is part of a growing global debate over who should have access to hundreds of millions of doses of vaccine that pharmaceutical companies are churning out in the US. Besides generating ill will, Biden’s insistence on an excess supply for America is potentially creating new openings for geopolitical rivals Russia and China.

A two-dose vaccine from AstraZeneca has received emergency clearance from the European Union and World Health Organization but not from the US. Now America’s partners are prodding Biden to release his supply, noting that the administration has lined up enough doses of three already-authorized vaccines to cover every American adult by the end of May and the entire US population by the end of July.

AstraZeneca says that the US-produced vaccines are “owned” by the U.S. government and that sending them overseas would require White House approval.

“We understand other governments may have reached out to the U.S. government about donation of AstraZeneca doses, and we’ve asked the U.S. government to give thoughtful consideration to these requests,” Gonzalo Viña, a spokesman for AstraZeneca, said in a statement.

Even though the 27-nation European Union is eager to relaunch a more fruitful trans-Atlantic relationship after the bruising Trump presidency, the vaccine issue is proving to be a thorny topic, with some in Europe seeing it as a continuation of former President Donald Trump’s “America First” focus.

EU member states’ ambassadors discussed the challenge this week. The German government said on Friday it was in contact with US officials about vaccine supplies but stressed that the European Commission has the lead when it comes to procuring shots for member states.

Biden and European Commission President Ursula von der Leyen have directed representatives to discuss supply chains in the vaccine production.

“Hopefully, we will be in a position on both sides of the Atlantic to ensure that sufficient quantities of vaccine doses are distributed out in line with the schedule so as to complete the vaccination campaigns,” EU commission chief spokesman Eric Mamer said.

Well over 10 million doses of AstraZeneca’s vaccine are stockpiled in the US for Americans.

“We want to be oversupplied and overprepared,” White House press secretary Jen Psaki said Friday, so Americans can still be swiftly vaccinated in the event of unforeseen issues with the existing production timeline.

“We have not provided doses from the US government to anyone,” she said.

Asked about the stockpiled vaccine, White House Covid-19 coordinator Jeff Zients said, “We have a small inventory of AstraZeneca so, if approved, we can get that inventory out to the American people as quickly as possible.” He said the US was following the same procedure it used for the already-authorized vaccines.