The United Kingdom has confirmed that one of its Royal Navy nuclear-powered submarines surfaced close to the Yantar, a notorious Russian spy ship late last year, to make it clear it was being observed.

A Russian ship in the North Sea is being monitored by the British and Dutch navies after it was spotted earlier this week, broadcaster NOS said on Thursday. The vessel, the Yantar, is used for gathering intelligence and mapping underwater infrastructure,

The UK authorized the British submarine to surface closely to the Russian vessel to warn it off, British defense secretary Healey said.