Tokyo might promise Moscow that returning the disputed islands off Hokkaido to Japan will not mean that U.S. military forces will be stationed there in line with Japan-U.S. security arrangements, diplomatic sources have said.

Tokyo believes such a promise will facilitate negotiations on the long-simmering dispute because Russia is particularly sensitive about U.S. military moves.

The idea has surfaced ahead of Russian President Vladimir Putin’s trip to Japan in December. Japan sees the visit as a chance to make progress on the decades-old territorial row, which has prevented the two countries from concluding a peace treaty to formally end World War II.

The inhabited Russian-held islands are Etorofu, Kunashiri, Shikotan and the Habomai islet group.

According to the sources, Russia has told Japan it stands by the 1956 Japan-Soviet Joint Declaration, which states Moscow will hand over smaller Shikotan and the Habomai group after concluding a peace treaty with Japan.

But it is also concerned U.S. military forces might be stationed on Shikotan and Habomai after they are returned, based on Article 5 of the Japan-U.S. security treaty. The article allows U.S. troops to be stationed in territories administered by Japan.

The government is studying what kind of impact there would be if Shikotan and Habomai, or possibly all the disputed islands, are exempted from the Article 5 application, the sources said Saturday.

Both the Japanese and Russian governments are aware that the issue of the Japan-U.S. security treaty is of paramount importance in the dispute, according to the sources.

One of the sources said Abe might go as far as making a widespread announcement saying that the territories in dispute do not fall under Article 5 of the treaty.

“A realistic scenario is that the prime minister shows his political will and seeks consent from the United States,” the source said.

Tokyo has no plan to seek a revision to the Japan-U.S. security treaty to allow special treatment for the islands.

But asking the United States to exempt them from Article 5 could be controversial at a time when Washington remains at odds with Russia’s military involvement in Ukraine and Syria, the sources said.

“Russia won’t agree to hand over (the islands) unless the possibility of stationing the U.S. military there is ruled out,” a source familiar with Japanese-Russian ties said.

For Russia, the area around the disputed islands is of “extremely high importance” because it faces Sea of Okhotsk, a Japanese government source said.

According to Japan’s Defense Ministry, Russia has deployed nuclear submarines armed with ballistic missiles in the Sea of Okhotsk to deter America’s atomic arsenal.

Many experts believe Russia’s strategic nuclear advantage in the area could be considerably undermined should the U.S. ever deploy military forces on the disputed islands. A foreign military force on those islands would be able to block the Russian military from using a key access route to the Pacific Ocean, they say.

But one government source said it would be very tough to persuade the U.S. to accept such a condition.

“It could even shake the foundations of the (Japan-U.S. military) alliance,” the source said on condition of anonymity.