European Commission's President Ursula von der Leyen on Saturday threatened to block exports of AstraZeneca COVID-19 vaccine if the European Union (EU) does not receive what it was promised.

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The official said AstraZeneca has only delivered 30 percent of the 90 million vaccines promised to the EU by the first quarter of 2021.

The contract with the Swedish-British lab calls for the delivery of vaccines manufactured in EU member countries and the United Kingdom, from which the EU has not received a single dose yet.

The drugmaker argued it had production delays in its European facilities, therefore it could only deliver 100 out of 350 million vaccines committed for the first half of 2021.

However, the UK received all the promised doses, which prompted Von der Leyen to write a letter of protest to AstraZeneca.

The European Union adopted a vaccine export control mechanism in January and last week extended its deadline until the end of June.

The mechanism has already been applied once by Italy, which blocked a 250,000 doses export to Australia, based on the persistent shortages and supply delays.