Europe's fight to secure COVID-19 vaccine supplies intensified on Thursday when the European Union warned drug companies such as AstraZeneca that it would use all legal means or even block exports unless they agreed to deliver shots as promised.

The EU, whose member states are far behind Israel, the United Kingdom and the United States in rolling out vaccines, is scrambling to get supplies just as the West's biggest drugmakers slow deliveries to the bloc due to production problems.

As vaccination centres in Germany, France and Spain cancelled or delayed appointments, the EU publicly rebuked Anglo-Swedish drugmaker AstraZeneca for failing to deliver and even asked if it could divert supplies from Britain.

European Council President Charles Michel said in a letter to four EU leaders that the EU should explore legal means to ensure supplies of COVID-19 vaccines it contracted to buy if negotiations with companies over delayed deliveries are unsuccessful.

"If no satisfactory solution can be found, I believe we should explore all options and make use of all legal means and enforcement measures at our disposal under the Treaties," Michel said in the January 27 letter.

EU rules on monitoring and authorising exports of COVID-19 vaccines in the 27-nation bloc could lead to exports being blocked if they violated existing contracts between the vaccine maker and the EU, an EU official said.

The European Commission is to lay out the criteria under which such exports would be evaluated on Friday.

The swiftest mass vaccination drive in history is stoking tensions across the world as big powers buy up doses in bulk and poorer nations try to navigate a financial and diplomatic minefield to collect whatever supplies are left.

Israel is by far the world leader on vaccine rollout per head of population, followed by the United Arab Emirates, the United Kingdom, Bahrain and the United States. Behind them are Italy, Germany, France, China and Russia.

The African Union (AU) has secured another 400 million doses of the AstraZeneca COVID-19 vaccine, a regional health leader said on Thursday, in a push to immunize 60 percent of the continent's population over three years.

Under fire from the EU, AstraZeneca CEO Pascal Soriot said the EU was late to strike a supply contract so the company did not have enough time to iron out production problems at a vaccine factory run by a partner in Belgium.

Tensions have risen as both New York-based Pfizer and AstraZeneca, headquartered in Cambridge, England, have had production problems.

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Britain, which has repeatedly touted its lead in the vaccine rollout race since leaving the EU's orbit on January 1, said its deliveries must be honoured.

"I think we need to make sure that the vaccine supply that has been bought and paid for, procured for those in the UK, is delivered," Minister for the Cabinet Office Michael Gove told LBC Radio.

Just a day ahead of a decision by European regulators on whether to approve the drugmaker's shot, Germany's vaccine committee said AstraZeneca's vaccine should only be given to people aged between 18 and 64.

"There are currently insufficient data available to assess the vaccine efficacy from 65 years of age," the committee, also known as Stiko, said in a draft resolution made available by the health ministry on Thursday.

Britain's Johnson said health authorities in Britain believed the vaccine was safe and worked across all age groups.

In the northern French region of Hauts-de-France, France's second-most-densely-populated region, several vaccination centres were no longer taking appointments for a first jab. In several other French regions, some online appointment platforms closed booking options.

Spain's Madrid region has ceased first vaccinations for at least this week and next and was using the few doses it has to administer second shots to those who have had the first one, said deputy regional government chief Ignacio Aguado.

Germany's most populous state, North Rhine-Westphalia, last week postponed opening its vaccination centres until February 8, while the state of Brandenburg has also had to push back vaccination appointments originally scheduled for the end of January due to delivery delays.

AstraZeneca is prepared to publish the delivery contract it has with the European Union and aims on Friday to make proposals to the European Commission on which sensitive parts to black out, the Frankfurter Allgemeine reported.

The newspaper quoted an EU source as saying that while AstraZeneca would not be able to deliver the 80 million doses expected for the first quarter, volumes should significantly exceed the 31 million doses that had earlier been reported.