HELSINKI, May 28 (Reuters) - The Finnish Border Guard said on Thursday it had not been able to confirm the presence of a suspected submarine near Helsinki last month.
In a rare incident, the military in April fired handheld underwater depth charges as a warning against what it suspected was a submarine in waters near the capital.
The Border Guard completed its investigation on Thursday by saying that part of the detected underwater sounds had a natural explanation, but the presence of a submarine or other underwater activity could not be completely excluded.
Finland, which shares an 833 mile (1,340 km) border with Russia, has been increasingly worried about its powerful neighbour after a year of Russian air force sorties and military border exercises. (Reporting By Anna Ercanbrack; Editing by Jussi Rosendahl and Hugh Lawson)