A decades-old territorial row may be taking a new turn as Japan and Russia look set to uphold a 1956 joint declaration in which Moscow promised to hand over two of the disputed islands to Tokyo once a peace treaty was signed.

Japanese Prime Minister Shinzo Abe agreed with Russian President Vladimir Putin during a summit Wednesday in Singapore that they will accelerate peace treaty talks based on the document, in which Moscow vowed to return Shikotan and the Habomai islet group.

The dispute over the islands off Hokkaido, seized by the Soviet Union following Japan's surrender in World War II in 1945, has long been a thorn in bilateral relations, preventing them from concluding a postwar peace treaty.

(Photo shows a part of Shikotan Island)

The latest agreement is seen as a change in Tokyo's stance to demand Russia return all of the islands and political analysts call it a "realistic" approach to break the gridlock.

However, the Japanese government maintains Wednesday's agreement between Abe and Putin does not signal a change in Tokyo's policy of resolving the sovereignty issue of all the disputed islands before concluding a peace treaty.

"Absent an agreement on the territory issue, there will be no peace treaty signed," a government source said.

The outlook for quick and tangible progress is far from certain.

Experts on Japan-Russia relations say it remains to be seen how serious Putin will be and that Tokyo will be required in forthcoming talks to maintain a delicate balance between Russia and the United States -- Japan's longtime security ally.

"President Putin and I share a strong resolve that it be us who put an end to the issue that has been left unresolved for more than 70 years after the war," Abe told reporters Wednesday after what he described as an "in-depth" discussion with the Russian leader.

Putin has acknowledged the legal validity of the 1956 declaration between Japan and the Soviet Union, which was meant to end wartime hostilities and restore diplomatic ties.

"The importance of the agreement in Singapore is that it signals Abe's willingness to compromise on this issue. It shows that he is a supporter of the idea of 'two plus alpha,'" said James Brown, an associate professor at Temple University's Japan campus.

Brown, an expert on Japan-Russia relations, said the tactic is aimed at recovering Shikotan and the Habomai islet group first and seek "some form of enhanced access" to the other two islands -- Etorofu and Kunashiri. They are known as the Northern Territories in Japan and the Southern Kurils in Russia.

But Brown believes it is a "fairy tale."

"To receive the smaller islands, Japan needs to accept that the two larger islands have been lost forever," he said.

The roughly 90-minute talks came after Putin abruptly proposed in September that the two countries conclude a peace treaty "without any preconditions" by year-end.

While Japanese officials sought to discover the true intention of the Russian leader's message, Abe said a series of one-on-one meetings with Putin would be important. Wednesday's summit was their 23rd direct talks.

Takashi Kawakami, a professor well-versed in security policy at Takushoku University, said the latest development reflects Putin's strategy to "drive a wedge" in the Japan-U.S. alliance.

Russia is concerned about possible U.S. military presence on the islands if the handover of Shikotan and the Habomai group of islets materializes, so Tokyo and Moscow would also have to take up that sensitive and difficult issue in future negotiations, Kawakami said.

Abe, who has been building a rapport with Putin, is promoting joint economic activities on the islands, even as the Russian leader's remarks in September were interpreted as his frustration over a lack of progress on the economic front.

Russia, for its part, is critical of Japan's imposition of sanctions in response to its 2014 annexation of Ukraine's Crimea region and vigilant against the planned deployment of U.S.-developed Aegis Ashore missile defense systems in Japan.

Abe said he will visit Russia in early 2019 to advance bilateral talks.

"For peace treaty talks to advance, Abe needs to put Japan's relations with Russia as well as those with the United States in the same equation," Kawakami said. "It won't be an easy task."