Prime Minister Shinzo Abe and Russian President Vladimir Putin on Saturday appointed their foreign ministers to oversee negotiations for concluding a bilateral postwar peace treaty based on a 1956 joint declaration.

Foreign Minister Taro Kono and his Russian counterpart Sergey Lavrov plan to hold talks before Abe’s planned trip to Russia in January for another summit, a senior Japanese official said after an Abe-Putin meeting on the margins of a Group of 20 summit in Buenos Aires.

The leaders also tapped Takeo Mori, a senior Japanese deputy foreign minister, and Russian Deputy Foreign Minister Igor Morgulov as their “special representatives” to carry out negotiations, according to the official.

A Kono-Lavrov meeting will be the first round of negotiations since Abe and Putin agreed during a meeting last month in Singapore to accelerate negotiations based on the 1956 declaration.

The document, approved by the parliaments of Japan and the Soviet Union, says the island of Shikotan and the Habomai islet group — two of four Russian-held islands off Hokkaido — will be handed over to Japan following the conclusion of a peace treaty.

“We would like to have solid discussions based on the result of summit talks in Singapore,” Abe said at the Buenos Aires meeting, part of which was open to the media.

The two governments plan to conduct joint economic activities on the four disputed islands as part of confidence-building measures, and Abe said, “I would like to promote cooperation in all kinds of fields so that we can elevate Japan-Russia relations to new levels.”

Putin, speaking through an interpreter, said he “uses every opportunity to confirm the development of Russia-Japan cooperative relations.”

Speaking at a news conference in Argentina’s capital, Putin said more details on what he called a “new mechanism” for resolving the peace treaty issue “will be provided later,” according to Russia’s Tass news agency.

Putin was quoted by Tass as saying Abe will visit Russia early next year.

“Maybe I will get a chance to visit Japan as well,” the president said, a comment taken as suggesting his participation in a G20 summit to be held next June in Osaka.

In the meeting, Abe and Putin agreed to strengthen bilateral cooperation in security.

Abe, however, expressed his concern about Russia’s recent seizure of three Ukrainian naval vessels and crews near the Crimean Peninsula, a territory Moscow unilaterally annexed from Kiev in 2014.

Abe told Putin that he hopes the situation will de-escalate through measures such as an early release of crew members.

The Japan-Russia territorial dispute, which also involves Kunashiri and Etorofu islands, has prevented Tokyo and Moscow from signing a post-World War II peace treaty.

Abe has emphasized that the Nov. 14 agreement to speed up talks based on the 1956 declaration would not run counter to Japan’s long-held policy of resolving the issue of the status of the four islands before signing a peace treaty.

His focus on the accord indicates he may prioritize the handover of Shikotan and Habomai, and continue negotiations for the status of the two other islands and conclusion of the treaty.

The islands, known as the Northern Territories in Japan and the Southern Kurils in Russia, were seized by the Soviet Union after Japan’s surrender in the war on Aug. 15, 1945.