The European Union is planning to extend its export authorisation scheme for Covid-19 vaccines to the end of June, two EU sources told Reuters on Thursday, in a move that could reignite tensions with countries who rely on shots made in the EU.

The mechanism was set up at the end of January as a reaction to vaccine makers' announcements of delays in the deliveries of Covid-19 vaccines to the EU.

It is due to expire at the end of...