LONDON, United Kingdom (AFP) — British Defense Secretary John Healey told parliament Wednesday the Royal Navy tracked a "Russian spy ship" that passed through UK waters, warning Russia's President Vladimir Putin: "We know what you're doing."

Healey said the Yantar (Amber) vessel was being "used for gathering intelligence and 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 members of parliament.

The ship entered British waters on Monday about 72 kilometers off the country's coast, with the Royal Navy dispatching two vessels to monitor it, Healy said.

"It was detected loitering over UK critical undersea infrastructure," the defense minister said.

He added the ship was now in the North Sea, "having passed through British waters."

A French official told Agence France-Presse that French military resources had also been mobilized to monitor Yantar but the ship "had no proven hostile intent."

"It happens regularly that a Russian vessel passes through and there is always close surveillance that is put in place," the official added.

Healey said it was the second time the Yantar had been detected in British waters recently, after it was also spotted in November.