Japan will consider retaliating against Russia's granting of fishing rights to other countries in waters around Russian-held islands claimed by Japan, Chief Cabinet Secretary Yasuo Fukuda said Thursday.

"We will carefully study the issue, including the question of whether to take countermeasures," the top government spokesman said at a news conference.

The comments follow Wednesday's revelation that Russia granted North Korea and a Ukrainian fishing firm permission to fish for saury in the area, which Tokyo says is within its exclusive economic zone.

Along with South Korea, there are now three countries with Russian permission to fish in the disputed waters.

"The situation is truly regrettable," Senior Vice Foreign Minister Seiken Sugiura told a separate news conference. "We have strongly protested to Russia, but Japan does not have diplomatic ties with North Korea so there is a limit to what specific actions we can take toward it."

The government is trying to get confirmation from Kiev that the Ukrainian firm has transferred its fishing rights to Taiwan fishers, Sugiura said.

The situation is complex, however, as the Ukrainian firm was possibly used as a dummy by Taiwan to gain Russia's permission to fish in the area, he said.

Meanwhile, Hideaki Kumazawa, vice minister of agriculture, forestry and fisheries, indicated it would be difficult to take action against North Korea because Tokyo does not recognize it as a state.