The European Union is asking AstraZeneca to publish the contract it signed with the bloc on Covid-19 vaccine supplies after the company's chief executive revealed confidential clauses, Reuters reported quoting an EU official.

In an interview with newspapers on Tuesday, AstraZeneca CEO Pascal Soriot said the EU contract was based on a best-effort clause and did not commit the company to a specific timetable for deliveries.

The interview followed the company's announcement of a cut in supplies to the EU in the first quarter.

The EU official said on Wednesday that the best-effort clause was standard in contracts with manufacturers of products that are in development.