bbc
The UK defence secretary, John Healey, says three Russian submarines carried out a "covert" operation in the Atlantic, north of the UK, lasting longer than a month.
He says he deployed a warship and aircraft in response, and the Russian vessels were "monitored 24/7".
He says there is "no evidence" of any damage to UK infrastructure in the Atlantic.
"Our armed forces left them in no doubt that they were being monitored, that their movements were not covert, as President Putin planned, and that their attempted secret operation had been exposed," says Healey.
And in a message to Putin, he adds: "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".