The Swedish military has called off its week-long search for a suspected submarine in the sea south of Stockholm, officials say.

Naval vessels and planes have been searching the Stockholm archipelago for the last week, amid suspicions a Russian submarine was in trouble there.

Russia’s defence ministry denied any of its ships were involved.

The vessel, whatever it was, is now believed to have left Sweden’s territorial waters.

The Swedish operation was reported to have been the country’s biggest military mobilisation since the Cold War.

In a statement, the military said (in Swedish): “This means the bulk of ships and amphibious forces have returned to port.” It added that some smaller units would remain in the area.

Rear Admiral Anders Grenstad told reporters: “We assess that the [vessel] that violated our waters has now left.”

“It’s the assessment of the defence forces that probably foreign underwater activity has taken place in Stockholm’s inner archipelago,” he said, calling any such activity within Swedish territory “unacceptable.”

The military believed at least one vessel was involved, he said, adding that it was probably not a large submarine, but “a small vessel.”

Image: Swedish corvette HMS Helsingborg (photo: Daniel Klintholm/Swedish Armed Forces)