The ministry said the two Japanese trawlers later returned to their home port with what appeared to be up to 20 bullet marks on their hulls.

Yasuaki Tanizaki, the ministry's European affairs chief, said the boats had been fishing in an area agreed on by the two countries.

Japan and Russia have yet to sign a peace treaty ending hostilities after the Second World War because they both lay claim to islands which were seized in 1945 by Soviet troops, who then expelled Japanese residents.

In 2006, a Japanese fisherman on a crab fishing boat was killed by a stray bullet fired as a warning by Russian border guards.