LONDON (REUTERS) - British foreign minister Dominic Raab accused the European Commission of brinkmanship over its threat to ban exports of Covid-19 vaccines, calling for Commission head Ursula von der Leyen to explain her comments.

The European Union on Wednesday (March 17) threatened to ban exports of Covid-19 vaccines to Britain to safeguard scarce doses for its own citizens, with von der Leyen airing frustration over a lack of deliveries from AstraZeneca plants in Britain.

"I think it takes some explaining because the world's watching... It also cuts across the direct assurances that we had from the Commission," Raab told Reuters.

"We expect those assurances and legal, contracted supply to be respected."

He said von der Leyen's comments contradicted assurances he had been given by Commission Vice-President Valdis Dombrovskis and by EU foreign policy chief Josep Borrell.

"We were reliably informed that they weren't aware of any plans to restrict lawfully contracted supply to the UK," Raab said.

But a Commission official said Dombrovskis made clear in his phone call with Raab that the aim of the EU's export authorisation system was to ensure that deliveries to EU countries were not disproportionately affected by exports.

"Dombrovskis invited the British government to provide figures on its exports of vaccines to the EU, which we look forward to receiving," the Commission official said, pointing out the EU had exported 10 million vaccine doses to Britain, but received none.

Britain has the fifth highest death toll from the coronavirus pandemic, but has one of the quickest vaccine rollouts among large countries, with over 25 million people given a first dose of a Covid-19 vaccine.

The government says it is on course to have given a first Covid-19 shot to half of all adults within the next few days, hitting the milestone much quicker than European counterparts.

Raab said that the European Union had previously agreed with Britain that during a pandemic, it was "wrong to curtail or interfere with lawfully contracted supply".

"Keeping supply chains open, keeping trade and vital supplies of medical equipment and vaccines is critically important," he said.

"We've all been arguing for this."