The vaccine producer 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 evening.
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," Mrs 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.
Mr Johnson also warned that a ban that extended beyond AstraZeneca's disputed supply could also block jabs produced for BioNTech/Pfizer in Belgium.
But Mrs 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.
Meanwhile, French President Emmanuel Macron backed the EU's export controls and said the summit marked "the end of naivety" from the bloc.
"I support the fact that we must block all exports for as long as some drug companies don't respect their commitments with Europeans," he said.
Mr Macron earlier expressed frustration at the slow pace of much of Europe's vaccine rollout. "We didn't shoot for the stars," he told the Greek television channel ERT before the summit. "We were wrong to lack ambition."
German Chancellor Angela Merkel also said the EU "not only supplies itself, but also exports to the world - in contrast to the US and Great Britain".
Dutch Prime Minister Mark Rutte said while his fellow leaders had found the Commission's tougher export measures "acceptable", he hoped they would never be used - a message echoed by his Belgian counterpart, Alexander De Croo.
Both those two countries are home to factories involved in the production of the AstraZeneca shot, which it's suggested may soon be sending increased supplies to European nations - a move that may assuage some EU anger, BBC Brussels correspondent Nick Beake reports.
Credit: The BBC