The EU has warned it will tighten exports of Covid vaccines produced in the bloc, amid a row with AstraZeneca over a cut in planned supplies.
Last week, AstraZeneca told the EU it was falling behind on its supply target because of production problems.
Pfizer-BioNTech has also said supplies of its vaccine will be lower, slowing down the EU's vaccination drive.
Vaccine supply has become a critical issue as nations seek to stem high infection rates.
The AstraZeneca row could affect supplies to the UK of the Pfizer-BioNTech vaccine, which has been developed by the US and Germany. Pfizer's Belgian plant supplies the UK.
Responding to the EU's comments, the UK's Minister for Covid Vaccine Deployment Nadhim Zahawi said on Tuesday that supplies were "tight" but added: "I'm confident that [AstraZeneca and Pfizer-BioNTech] will both deliver for us the quantities that we need to meet our mid-February target and of course beyond."
EU Health Commissioner Stella Kyriakides had earlier said the 27-member EU bloc would "take any action required to protect its citizens".
Companies making Covid vaccines in the EU would have to "provide early notification whenever they want to export vaccines to third countries", she said. The UK has now left the EU.
Mr Zahawi warned against what he called "the dead end of vaccine nationalism", adding: "No-one is safe until the whole world is safe."
The EU has already faced criticism for the slow rollout of vaccines, which it buys on behalf of all member states.(BBC)