A senior Russian security official warned Britain on Wednesday not to sail its warships near Crimea again unless it wants its sailors to get hurt.
The warning by Mikhail Popov, deputy secretary of Russia's Security Council, follows an incident last month when British warship HMS Defender exercised what London said were internationally recognised freedom of navigation rules in Ukrainian territorial waters near Crimea.
Russia annexed Crimea from Ukraine in 2014 and says the waters around it belong to Moscow despite most countries continuing to recognise the peninsula as Ukrainian.
It protested strongly against the British move at the time, with a coastguard vessel firing warning shots, and summoned the British ambassador for an explanation.
Mr Popov, in an interview in the state Rossiyskaya Gazeta newspaper, said Britain's behaviour and subsequent reaction to the incident were bewildering.
In particular, he criticised suggestions from British Prime Minister Boris Johnson and Foreign Secretary Dominic Raab that the incident could be repeated.
"Similar actions will be thwarted with the harshest methods in future by Russia regardless of the violator's state allegiance. We suggest our opponents think hard about whether it's worth organising such provocations given the capabilities of Russia's armed forces," said Mr Popov.
"It's not the members of the British government who will be in the ships and vessels used for provocative ends," he added. "And it's in that context that I want to ask a question of the same Boris Johnson and Dominic Raab - what will they say to the families of the British sailors who will get hurt in the name of such 'great' ideas?"