Drugmaker AstraZeneca must "catch up" on its promised deliveries to the EU before exporting doses elsewhere, the bloc's chief has said.
"The company... has to honour the contract it has with member states," European Commission President Ursula von der Leyen said on Thursday, reports the BBC.
She spoke after EU leaders held a summit to discuss vaccine supplies.
Meanwhile, French President Emmanuel Macron told reporters this marked "the end of naivety" from the EU.
Vaccine rollouts in European Union states have started sluggishly, and the bloc has blamed pharmaceutical companies - primarily AstraZeneca - for not delivering promised doses. AstraZeneca has denied that it is failing to honour its contract.
"I think it is clear that first of all the company has to catch up," von der Leyen told a news conference after the virtual leaders summit.
"[It] has to honour the contract it has with European member states before it can engage again in exporting vaccines," she said. "We want to explain to our European citizens that they [can] get their fair share."The EU has been criticised, primarily by the UK and the World Health Organization (WHO), for so-called vaccine nationalism after it introduced export controls on jabs produced within the bloc.
In response, UK Prime Minister Boris Johnson warned that "blockades" were not "sensible".
He said that a ban would imperil the UK's vaccination drive, which has so far been more successful than most EU member states' vaccine programmes.
Johnson also warned that a ban that extended beyond AstraZeneca's disputed supply could also block jabs produced for BioNTech/Pfizer in Belgium.
But von der Leyen hit back on Thursday, arguing that the EU was the "region that exports most vaccines worldwide".
"We invite others to match our openness," she said. The EU chief earlier tweeted that the EU had exported some 77 million doses to 33 countries since December,
Her comments came a day after the EU issued a joint statement with the UK in which both sides pledged to work together after weeks of tensions over the Oxford-AstraZeneca jab.