Japan's Foreign Ministry on Sunday issued a protest after Russian border guards opened fire at two Japanese fishing vessels off the disputed South Kuril islands.

The border guards fired warning shots from a helicopter and then had to open direct fire at the Japanese fishing vessels on Friday when the trawlers refused to stop after entering Russia's territorial waters off Kunashir Island, the Russian coastal guard service said.

The fishing boats returned to their port of Rausu with numerous bullet holes on their hulls, the Japanese Foreign Ministry said, adding that the border guards' actions could have resulted in the loss of life and were completely inappropriate.

The ministry also said the vessels were fishing under bilateral agreements and urged Russia to take measures to avoid such incidents in the future.

Tokyo's continued claim over four South Kuril Islands (Iturup, Kunashir, Shikotan, and Habomai) has so far prevented Russia and Japan from signing a formal peace treaty to end World War II hostilities.

The four southern islands of the chain to the northeast of Japan were annexed by the Soviet Union after World War II.

TOKYO, January 31 (RIA Novosti)