The Russian Embassy in London said that Russia posed no threat to undersea cables in Britain and other NATO countries, after UK defence minister John Healey accused Moscow of "malign activity" at sea.

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.

The Royal Navy has been monitoring a Russian spy ship after it was spotted around UK waters earlier this week, the defence secretary has told MPs. John Healey said the vessel, Yantar, was used for gathering intelligence and mapping the UK's critical underwater infrastructure.

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