MOSCOW — Ships and helicopters of the Swedish Navy searched intensively over the weekend in coastal waters after detecting what the military said were signs of “foreign underwater activity” near the capital, Stockholm.

A Swedish newspaper reported that the military had detected radio signals from a Russian submarine that was perhaps stranded underwater by an emergency.

The development, if confirmed, would have far-reaching implications for highlighting how military tensions between Russia and the West have escalated over the crisis in Ukraine.

Military brinkmanship in the Baltic Sea has risen to near Cold War levels, as NATO has deployed additional forces to the area and Russia has stepped up exercises along its borders. Russia denied on Sunday that any of its submarines were missing.