A memorial ceremony has been held in the northern Japanese city of Rumoi in Hokkaido to mourn the more than 1,700 people who died when three ships were attacked by what appeared to be Soviet submarines in 1945.

About 50 people attended the ceremony held on Monday, 77 years since the incident.

On August 15, 1945, Japan announced its surrender in World War Two, just a week before the incident.

The ships were transporting Japanese nationals from Sakhalin Island in Russia's Far East when they were attacked with torpedoes and shelling from submarines. Japan had ruled the southern part of Sakhalin.

Documents found in the 1990s indicate that the attacks were conducted by Soviet forces.

But the Japanese and Russian governments have not confirmed the facts.

The head of a group of bereaved families said that although neither government has officially acknowledged what actually happened, it's the group's mission to pass down the incident to posterity and appeal for peace.

A woman said that although war seems like a distant memory, many people are being killed in Ukraine even now, and stressed the need to make efforts to prevent a recurrence.