Japanese Prime Minister Shinzo Abe and Russian President Vladimir Putin agreed Tuesday to accelerate talks on a postwar peace treaty that has not been concluded due to a territorial dispute, while suggesting the process will not be easy.

The summit in Moscow was held after the two agreed in November to step up their search for a solution on the basis of a 1956 joint declaration, which calls for the handover of two of four disputed isles off Japan's northernmost main island of Hokkaido.

"We confirmed our resolve to powerfully work (on the issue) under the leadership of myself and President Putin to find a solution acceptable to both countries," Abe, standing next to Putin, said in remarks to the press following the around three-hour meeting.

The countries' foreign ministers, tasked with overseeing the peace treaty negotiations, will meet in February in Germany for the second round of talks, Abe said.

The two leaders also vowed to enhance economic ties, with Putin proposing a 50 percent rise in the value of annual trade with Japan to around $30 billion (3.3 trillion yen) and increased efforts to realize joint economic activities on the four islands, known as the Northern Territories in Japan and the Southern Kurils in Russia.

But no substantive progress on the territorial row was announced after the leaders' 25th summit.

"It is not easy to solve problems that have been left more than 70 years after the end of the war," Abe said. Putin agreed that "painstaking" work toward concluding a peace treaty remains ahead, noting any treaty must have public support in both countries.

Abe is keen to resolve the dispute over the islands that have remained under Russian control since the end of World War II and to make a peace deal the main pillar of his political legacy. The Japanese leader is believed to be pursuing a June timeline to reach a broad agreement with Putin, who is expected to visit Japan that month for the Group of 20 summit.

The 1956 declaration, which ended the state of war between the nations and restored diplomatic ties, stipulated the handover by the Soviet Union to Japan of Shikotan Island and the Habomai islet group following the conclusion of a peace treaty.

But the two countries differ over what a "handover" of the two islands would mean, with Tokyo arguing that it should entail Japan assuming sovereignty and Moscow asserting nothing relating to sovereignty is mentioned in the document.

Japan maintains that all of the islands are "inherent territories" of the country that were "illegally occupied" by the Soviet Union following Tokyo's surrender in World War II in 1945, while Moscow insists it legitimately acquired them as a result of the war.

With Moscow increasingly viewed as unlikely to cede the two larger islets, called Kunashiri and Etorofu in Japan, Japanese government sources said Abe is leaning toward accepting a peace pact with Russia if the handover of the two smaller islets is assured.

As Japan has long sought the return of all of the Northern Territories, such a shift could trigger a public outcry.

Russia, for its part, is concerned that the United States could deploy troops on Shikotan and the Habomai islet group if they are transferred to Japan.

Abe said on a New Year TV program that the presence of the U.S. military in Japan contributes to peace and stability around the country and does not pose a threat to Russia.

Reflecting Moscow's concern, diplomatic sources said the two countries are considering including in an envisioned peace treaty a clause ensuring that the countries will not adopt hostile military policies against each other.

But some officials in Japan are cautious about such a security provision as it could restrict the activities of the Japan-U.S. security alliance, according to the sources.

The Northern Territories cover about 5,000 square kilometers and adjacent waters contain rich fishing grounds. Nearly 17,000 Russians reside on Kunashiri, Etorofu and Shikotan, while the Habomai islet group is uninhabited.

Shikotan and the Habomai group account for only 7 percent of the total landmass of the disputed islands.

Rallies against the return of the two islands have taken place in Moscow and elsewhere in recent months, with some Russians saying if the territories are "sold" it would be a crime against the homeland.