Russia has been increasing its inspections of Japanese kelp fishing boats off a group of disputed islands this year, a fisheries body and other sources said Monday, in apparent retaliation for Tokyo's participation in international sanctions over the war in Ukraine.

Russian border security officials made 195 inspections of boats off the Habomai group of islets, off Hokkaido in northern Japan, in June and July, far higher than the 87 cases between June and September last year, the sources said. But there were no cases of any boats being seized.

Kelp fishing boats on the waters off the Habomai group of islets in June 2019 | KYODO

Kelp fishing boats on the waters off the Habomai group of islets in June 2019 | KYODO

Russian inspections of kelp fishing boats used to be rare but have increased in recent years and have risen significantly this season, said the Hokkaido Fisheries Association, which negotiates with Russia to determine the operating conditions for the boats including the fishing fees.

"We have to stop running our boats every time we get inspected, which hampers our work," said a fisherman in his 60s from Nemuro, Hokkaido.

The agreement on kelp fishing was first reached in 1963 with the Soviet Union.

This year's start of operations was pushed back by three weeks to June 22 as a result of the war in Ukraine.

Under the latest agreement, around ¥88 million ($627,000) was paid to the Russian side, which allowed 220 boats to harvest seaweed until Sept. 30.