STOCKHOLM (AFP) - Sweden called off early Friday the hunt for a suspected submarine that sparked one of the largest mobilisation of the Nordic country's naval forces since the end of the Cold War.

"At 8:00am Friday morning, the main part of the maritime intelligence operation which had been underway in the Stockholm archipelago since the previous Friday was concluded," the armed forces said in a statement.

"This implies that most naval and amphibious forces have returned to port and are back at the normal alert level. Minor field units with specific tasks remain in the area."

The week-long search in waters near the Swedish capital was said to be a hunt for a Russian submarine.

Reports last week of a "man-made object" in the water set off a search operation involving battleships, minesweepers, helicopters and more than 200 troops scouring an area about 30 to 60km from Stockholm.

The Swedish defence forces started officially scaling back the activities Wednesday, saying some ships had already returned to port.

While the Swedish military has been very careful not to point fingers directly at any foreign power, media speculation has centred heavily on the possibility that the object targeted in the hunt was a Russian submarine.

Russia has denied it was the source of the suspicious underwater activity, blaming a Dutch submarine for triggering the hunt, a claim rejected by the Netherlands.

The massive military operation has for many Swedes evoked memories of the 1980s, when the Nordic country's navy was in hot pursuit of suspected Russian submarines dozens of times.

But during more than a decade of Cold War submarine hunts, Sweden never succeeded in capturing one, except in 1981 when the U137 ran aground several miles from one of Sweden's largest naval bases, triggering an embarrassing diplomatic stand-off for Russia.