Japan's Defense Ministry said two Russian fighter jets briefly intruded into Japanese airspace Thursday off the northwestern tip of the island of Hokkaido, prompting Tokyo to lodge a protest.

Japanese air force jets scrambled after the intrusion by the two SU-27 jets off the coast of Rishiri island, which lasted just over a minute, ministry official Yoshihide Yoshida said.

Yoshida said it was not immediately known whether the airspace violation was intentional or accidental, but that it was "extremely problematic." The last intrusion by Russian jets in Japanese airspace was on Feb. 9, 2008, he said.

Japan's Foreign Ministry lodged a protest with the Russian Embassy in Tokyo.

Another ministry official who spoke on condition of anonymity said it was not immediately clear whether it was related to a government-sponsored rally held Thursday demanding that Moscow return a group of disputed islands off Hokkaido's eastern coast captured by the Russians in 1945.

Prime Minister Shinzo Abe told the rally that he will do his utmost to resolve the territorial dispute with Russia, which has kept the two nations from signing a peace treaty officially ending their hostilities in World War II.

Soviet troops captured the islands in the waning days of the war, forcing about 17,000 Japanese residents to be deported over the next few years. About 17,000 people, mostly Russians, live there now.

Japan has designated Feb. 7 as "Northern Territories Day," saying that a treaty dating back to that day in 1855 supports its claim to the islands, which are known in Russia as the Southern Kurils.

They lie as close as 10 kilometers (six miles) to Japan's Hokkaido island and are also near undisputed Russian territory. The islands are surrounded by rich fishing grounds and are believed to have offshore oil and natural gas reserves, plus gold and silver deposits.

Addressing former Japanese residents of the islands and others gathered in a large Tokyo concert hall, Abe said he told Russian President Vladimir Putin in December that he wants to settle the dispute. Abe plans to send former Prime Minister Yoshiro Mori as a special envoy to Russia this month, but prospects for progress on the issue are uncertain.

"We aim to finally resolve the problem with Russia on the disputed islands and realize the signing of a peace treaty," Abe said in a brief speech before being whisked back to parliamentary proceedings.

In 2010, former President Dmitry Medvedev became the first Russian or Soviet leader to visit the islands, triggering sharp rebukes from Tokyo. He visited a second time last July.

More than half of the former Japanese residents of the islands have died in the 68 years since the Russians took control.

"My birthplace is right in front of me, but I can't return" to live there, said Choriki Sugawara, a 79-year-old man who recalled happy memories growing up on the island of Kunashir _ called Kunashiri in Japan _ in a fishing family of eight.

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Associated Press writer Malcolm Foster contributed to this report.