Brussels will publish a redacted copy of its contract with drugs giant AstraZeneca on Friday, EU chief Ursula von der Leyen said, following a dispute over delays to vaccine deliveries.

"We want to publish it today. We are talking to the company about which parts have to be blacked out," she told German broadcaster Deutschlandfunk on Friday.

AstraZeneca has warned that there will be delays in its delivery of the coronavirus vaccine, despite what von der Leyen described as a "crystal clear" commitment.

The firm's CEO, Pascal Soriot, has said there have been production glitches in AstraZeneca's plants operated by subcontractors in the EU, and that the contract only called for it to make "best efforts" to hit targets.

But von der Leyen, building on increasingly angry comments from EU officials this week, insisted the contract committed the British-Swedish firm to fixed numbers of vaccines per quarter.

"The 'best effort' applies as long as it was not clear whether they could develop a vaccine. We have passed that time. The vaccine is there," she said.

But AstraZeneca was contracted to deliver its drug to EU governments beforehand, to allow a rapid roll out across the bloc, which fears a new wave of infections from Covid-19 variants.

"There are very clear delivery quantities, both for December of last year and for the coming quarters. These are in the contract," von der Leyen said.

AstraZeneca has continued to service its separate British contract, arguing that because that was signed with the UK government three months earlier there had been time to fix production issues for it.

But von der Leyen said that where the vaccines were produced was a matter for the firm, and its UK plants had clearly been part of the plan when it signed with Brussels.