BRUSSELS — Millions of coronavirus vaccine doses are in cold storage in the U.S. that can’t be injected in the states because they are not yet approved by the Food and Drug Administration, but the Biden administration is not yet allowing them to be sent overseas, where American allies are struggling to get enough doses for vulnerable populations.

The two-dose vaccine from AstraZeneca has received emergency approval from the European Union and World Health Organization, but not in the U.S. Now U.S. partners are prodding President Joe Biden to release the supply, noting that the administration has lined up enough doses of the three already-approved vaccines to cover every American adult by the end of May and the entire U.S. population by the end of July.

EU member states’ ambassadors this week discussed the challenge of accessing US-produced doses of the AstraZeneca shots. The German government said on Friday it was in contact with U.S. officials about vaccine supplies, but stressed that the European Commission had 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.

Asked whether the EU’s executive arm had asked AstraZeneca to deliver US-made doses of the vaccine to Europe, Mamer declined to provide details of discussions with the company.

Even though it is not approved in the U.S., well over 10 million doses of AstraZeneca’s vaccine are stockpiled in the country for domestic use and cannot be exported under the terms of the company’s agreement with the federal government.

Drug manufacturers that received federal assistance in developing or expanding vaccine manufacturing of doses were required to sell their first doses to the U.S. In the case of AstraZeneca, whose vaccine was initially expected to be the first to receive federal emergency use authorization, the U.S. government ordered 300 million doses — enough for 150 million Americans — before issues with the vaccine’s clinical trial held up its approval in the U.S.

As foreign regulators have moved ahead with approval for the shot, the U.S. has not dropped its contractual claim on the initial doses produced in the U.S.

That policy has also come under criticism from U.S. neighbors like Canada and Mexico, which have been forced to seek vaccine manufactured on a different continent, rather than across the border. Its enforcement comes as the Biden administration has purchased enough doses of Moderna, Pfizer and Johnson & Johnson to be able to inoculate 150 million more people than its population by the end of the year.

The U.S. has also ordered 110 million doses of vaccine from Novavax, which is expected to file for emergency approval as soon as next month.

“We want to be oversupplied and overprepared,” White House press secretary Jen Psaki said Wednesday, saying Biden wanted contingencies in the event of any unforeseen issues with the existing production timeline.

“We still don’t know which vaccine will be most effective on kids,” she added. “We still don’t know the impact of variants or the need for booster shots. And these doses can be used for booster shots as well as needed. Obviously that’s still being studied by the FDA but again we want to be over-prepared.”

Pressed Thursday on the AstraZeneca situation, Psaki said, “We have conveyed privately what we’ve conveyed publicly, which is that our focus is on ensuring the American people are vaccinated.

Asked about the surplus Wednesday, Biden told reporters that “if we have a surplus, we’re going to share it with the rest of the world.”

“This is not something that can be stopped by a fence no matter how high you build a fence or a wall. So we’re not going to be ultimately safe until the world is safe,” acknowledged Biden. “So, we’re going to start off making sure Americans are taken care of first, but we’re then going to try to help the rest of the world.”

AstraZeneca’s 30,000-person U.S. trial didn’t complete enrollment until January. The company hasn’t given any hints of when initial results might be ready beyond an executive with AstraZeneca’s U.S. division’s statement to Congress last month that he expected it would be “soon.”

Amid its own stumbling vaccine rollout, the EU appears increasingly resigned to the Biden administration retaining control of the doses.

Even though the 27-nation bloc is eager to relaunch a fruitful trans-Atlantic relationship after the bruising Trump presidency, cooperation between the EU and the US proves to be a thorny topic, with some in Europe seeing it as a continuation of former President Donald Trump’s “America First” approach.

The EU is at odds with AstraZeneca because the company is delivering far fewer doses to the bloc than it had promised. Of the initial order for 80 million doses to the EU in the first quarter this year, the company will be struggling to deliver half that quantity.

Despite shortages at home and often being accused of vaccine protectionism, the 27-nation bloc has allowed the export of well over 34 million doses of COVID-19 vaccines over the past weeks, including 953,723 shots to the United States.

Meanwhile, Russia and China, whose leaders don’t face voters in free and fair elections, have used their domestically produced shots for strategic leverage.

China has pledged roughly half a billion doses of its vaccines to more than 45 countries, according to a country-by-country tally by The Associated Press. Four of China’s many vaccine makers are claiming they will be able to produce at least 2.6 billion doses this year.

Russia has sent millions of doses of its Sputnik V vaccine to countries around the world, even as it vaccinates its own population. Analysts say a goal of this vaccine diplomacy is to bolster Russia’s image as a scientific, technological and benevolent power, especially as other countries encounter shortages of COVID-19 vaccines because richer nations are scooping up the Western-made versions.

Israel, which has vaccinated more than half of its population with Pfizer vaccines produced in Europe, has also attempted to use vaccine diplomacy to reward allies.

Biden did move to have the U.S. contribute financially to the United Nations and World Health Organization-backed COVAX alliance, which will help share vaccine with more than 90 countries with lower and middle-income nations, but it has yet to commit to sharing any doses.

In Washington, Psaki said that “in terms of the supply we have purchased, our first focus, our primary focus is on vaccinating the American people. That’s what we’ve conveyed publicly and privately, as well.”

The EU is facing a major political embarrassment in its slow rollout of vaccines, especially considering other nations like Britain, Israel and the U.S. are so far ahead of the bloc, even though the continent is a main hub of pharmaceutical producers.

The latest figures by Our World in Data show that the EU has vaccinated 10% of its targeted population, while the U.S. has covered 29% and the U.K. 35%.