Britain is willing to provide security or "backfill" fighter jets to any country that wants to send Russian or Soviet-era planes to Ukraine, British Defence Secretary Ben Wallace said on Friday.

Britain has sent ammunition and weapons to Ukraine and is currently training its troops to use British tanks, but it has baulked at suggestions from Ukrainian President Volodymyr Zelenskiy that it should also send fighter jets.

Wallace said one way for countries to quickly help Ukraine would be for those with MIG-29 or SU-24 jets to donate them to Kyiv.

"If they wish to donate, we could use our fighter jets as a backfill and provide security for them as a result, or indeed to backfill to allow them to have their own capability because they are already configured to fight in a NATO way, where of course Ukraine isn't," he told Times Radio.

Wallace said he was unsure if any country was willing to do that yet. (Reporting by Farouq Suleiman; writing by Kate Holton; Editing by Alex Richardson)