British Defense Secretary John Healey told parliament Wednesday the Royal Navy tracked a "Russian spy ship" that passed through U.K. waters, warning Russia's President Vladimir Putin: "We know what you're doing.

Royal Navy submarine used to warn off Russian spy ship loitering over cables - The nuclear-powered hunter-killer submarine surfaced close to the Yantar to let the Russian ship know it was being watched.

A Russian spy ship entered British waters twice in recent weeks, prompting the UK to deploy Royal Navy ships, Royal Air Force planes and a submarine, Defence Secretary John Healey said.

Defence secretary John Healey warned Vladimir Putin ‘we see you, we know what you are doing and we will not shy away from robust action’. | ITV National News

Moscow’s intelligence ship Yantar enters UK waters in ‘another example of growing Russian aggression’, according to the Defence Secretary

Returning to the Defence Secretary’s statement to Parliament earlier, John Healey said the UN “law of the open seas” means there are options “not available” to the Government in limiting foreign vessels in UK waters. It comes after Healey revealed that a Royal Navy submarine was used to warn off one of Vladimir Putin’s spy ships.

Britain said it monitored a Russian spy ship in the English Channel in recent days and would strengthen its response to secret operations by Russian ships and aircraft in an effort to protect undersea cables.