Japanese officials say they have high expectations for improved bilateral relations going into Friday’s summit between Prime Minister Shinzo Abe and his Russian counterpart Vladimir Putin, in which a long-standing territorial dispute and a potential visit to Tokyo by the Russian leader will likely be discussed.

The scheduled unofficial three-and-a-half hour meeting in the southern Russian city of Sochi comes at the end of Abe’s weeklong visit to Europe. He made stops in Italy, France, Belgium, Germany and Britain to lay the groundwork for the Group of Seven summit Japan is hosting later this month.

The unofficial nature of the stop, where there will be no official ceremonies or a joint news conference, is intentional, according to a high-ranking foreign ministry official, so Abe and Putin can hold frank, one-on-one talks.

The question is whether the two leaders can rebuild trust and momentum for negotiations that stalled after Russia’s annexation of Crimea in 2014. Japan, in solidarity with the United States and European nations, imposed sanctions on Russia following the invasion. Relations deteriorated even further after Russian Deputy Foreign Minister Igor Morgulov said last September that the territorial issue over the islands, called the Northern Territories in Japan and the Southern Kurils in Russia, was already resolved. The issue has prevented the two countries from signing a peace treaty to put an official end to their World War II conflict.

Before departing for Europe on Sunday, Abe had said, “We must sit down and talk in order to solve issues surrounding a peace treaty.”

Experts say the visit could set the final stage for the negotiations because the talks are being spearheaded by two leaders who have tremendous political capital and support at home.

“This is the continuation of the process that started in April 2013 when Abe visited, but the process was discontinued due to the Ukraine issues,” said Noboru Shimotomai, a professor at Hosei University. “The summit talks could allow both countries to talk about a peace treaty at a new level.”

The two leaders will also discuss strengthening economic cooperation between their respective countries. Russia’s economy has been hit hard by a plunge in oil prices.

Since the end of WWII, Japan and Russia have had a tenuous relationship due to the sovereignty dispute over the four islands in question that were seized by the then-Soviet Union at the end of the war and are controlled by Russia.

But Putin has raised hopes of resolving the issue in Japan with past comments. In March 2012, he said the two sides should accept hikiwake, a martial arts term meaning a tie or draw, over the issue.

Reaching a resolution is a political priority for Abe, whose father Shintaro Abe helped arrange then-President Mikhail Gorbachev’s first visit to Japan during his stint as foreign minister. Both leaders had also agreed to seek “a compromise acceptable to both sides” compromise over the sovereignty issue of the islands when they met in April 2013.

Tokyo and the Kremlin resumed high-level talks last October after Foreign Minister Fumio Kishida visited Moscow. Abe and Putin also talked on the sidelines of the Group of 20 summit in Turkey as well as over a conference call earlier this year.

In addition, Masahiko Komura, the vice president of Abe’s ruling Liberal Democratic Party, made a trip to Moscow in January followed by a similar trip by LDP policy chief Tomomi Inada in April. A foreign ministerial meeting between Kishida and his Russian counterpart Sergey Lavrov last month sent a public message that both sides are willing to work on the issue.

Abe’s continued efforts to reach out to Putin might have thawed the ice. The Russian president last month told reporters that the two leaders need to have an ongoing and uninterrupted dialogue, but that Japan decided to “limit contacts with us at one point.”

In a clear reference to the sanctions, Putin commended Japan for seeking to maintain relations with Russia despite pressure from the United States, saying “some kind of compromise can and will be found.”

Still, how to solve the issue and proceed with the peace treaty remains a problem. Neither Japan nor Russia clearly indicated what a compromise might look like.

Russia maintains that the four islands are rightly theirs, emphasizing the importance of the 1956 Japan-Soviet joint declaration stating that two of the islands, the Habomai and Shikotan islets group, will be returned to Japan after the signing of a treaty.

For its part, Japan maintains that a peace treaty can only be signed after the territorial dispute is settled.

Before the foreign ministerial talk last month, Lavrov said all four islands will be covered in the negotiations, but a peace treaty and the negotiations over the islands are not directly related. Lavrov stressed the 1956 declaration, while acknowledging the 2001 Irkutsk Statement in which Putin and then-Prime Minister Yoshiro Mori agreed on the validity of the 1956 declaration and said the two countries will also discuss the two islands of Etorofu and Kunashiri in order to sign a treaty.

The future of Etorofu and Kunashiri remain a hot issue in Japan. Kazuhiko Togo, a former director-general of the European Affairs Bureau who handled the negotiations at the foreign ministry, said Russia mentions the 1956 declaration whenever it is ready to make a compromise. Yet Togo said the declaration stirs fear and distrust among many in Japan that Etorofu and Kunashiri will be left out of the negotiation.

In fact, Togo said Tokyo rejected a so called 1992 secret proposal in which Moscow said it is prepared to conclude a treaty to transfer the islands of Hobomai and Shikotan and hold similar negotiations over Etorofu and Kunashiri before signing the peace treaty.

Yet Tokyo rejected the idea, insisting that there has to be a clearer guarantee that Etorofu and Kunashiri will be returned. Togo also said Japan’s best shot at negotiating a deal was right after the fall of the Soviet Union when Russia was relatively weak.

“If Japan continues to insist on getting the sovereignty of the four islands first, nothing is going to come out of the negotiations,” said Togo, now a professor at Kyoto Sangyo University. “A window of opportunity is open so long as Putin is willing to negotiate. But Japan has to grab the opportunity as Russia is also saddled with other important diplomatic issues such as China and the United States.”