The UK said on Wednesday that its Royal Navy had tracked the ship about 45 miles (72 kilometres) off its coast, saying the vessel was being used for "gathering intelligence".

"I do not have information on what this is about in detail. So I would not comment on this," Kremlin spokesman Dmitry Peskov said.

British Defence Secretary John Healy told parliament a day earlier that the Yantar ("Amber" in Russian) was also "mapping the UK's critical underwater infrastructure".

"I also wanted President Putin to hear this message: 'We see you, we know what you're doing and we will not shy away from robust action to protect this country'," he told MPs.

Healy said it was the second time the Yantar had been detected in British waters in recent weeks, after it was spotted in November.

Relations between Moscow and London have been frosty for years, with Russia singling out the UK as one of the most hostile Western countries, but have dipped to new lows since the Ukraine offensive.

The UK is one of Kyiv's staunchest allies.