If promised supplies of the Oxford University-AstraZeneca COVID-19 vaccine may not arrive first, European Commission President Ursula von der Leyen has threatened to halt exports.
In an expansion of the dispute, Von der Leyen said that Anglo-Swedish pharma giant AstraZeneca had only produced 30% of the 90 million vaccine doses promised for the first quarter of the year.
"We have the option of banning a planned export. That's the message to AstraZeneca – you fulfil your contract with Europe first before you start delivering to other countries," Von der Leyen told Germany's Funke media group.
The message comes as the EU struggles to accelerate its immunization programme, as many member countries face a third coronavirus wave and additional restrictions on public life.
The corporation blamed production delays at its EU facilities, but European officials are outraged that AstraZeneca was able to produce on its UK deal despite falling short on the continent.
In an interview with German media, Von der Leyen reiterated that the EU's deal with AstraZeneca specifies that vaccines for the EU will be manufactured in both EU and UK facilities.
"But we haven't received anything from the Brits, although we are delivering to them," she said, adding that the European Commission had sent a "formal letter" to the company to complain.
Since early February, EU-based producers have exported 41 million vaccine doses to 33 countries, according to Von der Leyen, rendering the EU one of the world's largest export regions for COVID-19 vaccines.
"I can't explain to European citizens why we are exporting millions of vaccine doses to countries that are producing vaccines themselves and aren't sending us anything back," she said.