Britain, Norway and other countries conducted a weekslong operation to deter Russian spy submarines near undersea cables in the North Atlantic, the U.K. defense chief said Thursday, accusing Moscow of using the distraction of the Iran war to ramp up malign activity against Europe.

Defense Secretary John Healey said a Royal Navy frigate, aircraft and hundreds of personnel were involved in tracking a Russian attack sub and two spy submarines operating north of the U.K., and prevented the spy vessels from carrying out “nefarious” operations.

He said the Russian vessels eventually left after the operation that lasted more than a month.

The U.K. said other allies were also involved, but didn't name them.

NATO countries have repeatedly expressed concern that Russia could use its fleet of spy ships to sabotage underwater cables on which global communications depend. Russia has dismissed those claims.

Healey said his message to Russian President Vladimir Putin was was “we see your activity over our cables and our pipelines and you should know that any attempt to damage them will not be tolerated and will have serious consequences.”

Norwegian Defense Minister Tore Sandvik said in a statement that Russia’s operation occurred in and near Norwegian and British maritime areas in recent weeks.

Norway and the U.K. said the activity was coordinated by Russia’s Main Directorate of Deep Sea Research, known as GUGI, which is part of Russian armed forces. The activity is a reminder that Russia is further developing its abilities to map and sabotage critical Western infrastructure at ocean depths, Norway's Defense Ministry said.

Healey said the subs are “designed to survey underwater infrastructure during peacetime and sabotage it in conflict.”

In November, Britain told Russia it was ready to deal with any incursion into its territory after the spy ship Yantar was detected on the edge of U.K. waters north of Scotland.

Healey said the submarine activity occurred in the U.K.’s exclusive economic zone, which extends for 200 nautical miles (230 miles, 370 kilometers) from shore, but not its narrower territorial waters.

British officials have tried to keep Russia in the international spotlight even as the world’s attention is focused on conflict in the Middle East. They have also stressed the overlap between conflicts there and in Ukraine, saying Russia has supplied Iran with drone parts and other support.

Healey told a news conference that “Putin would want us to be distracted by the Middle East,” but Russia is the main threat to the U.K. and its allies.

“We will not take our eyes off Putin,” he said.

In late March, the U.K. said its military was ready to seize ships suspected to be part of Russia’s “shadow fleet” of vessels shipping oil in violation of international sanctions over Moscow’s war on Ukraine. Previously, Britain had only helped France and the U.S. monitor ships before they were boarded.

“We are ready to take action" against the vessels, Healey said.