The head of the UK's armed forces also rejects Ukraine's call for a no-fly zone, saying it will not help.
Watch: We have a direct line to Moscow, says UK chief of defence staff Adm Sir Tony Radakin
On Britons wanting to join the fight, Adm Radakin said that the "sound of gunfire" was not "something you want to rush to", and urged people to support Ukraine in sensible ways from the UK. Last week the Chief of Defence People, Lt Gen James Swift, sent out a message to the chain of command stressing that UK military personnel were "not authorised" to travel there.
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