Russian President Vladimir Putin said Thursday that Japan’s security alliance with the United States continues to pose a threat, suggesting it remains a stumbling block to the signing of a postwar peace treaty between Tokyo and Moscow.

Putin said at an annual year-end news conference that a solution has yet to be found, reiterating concerns that the United States is seeking to deploy intermediate-range missiles in Japan following the expiration of an arms control treaty earlier this year.

The Intermediate-Range Nuclear Forces Treaty, signed by the United States and Russia in 1987, had banned land-based ballistic and cruise missiles with a range of 500 to 5,500 kilometers.

Putin meanwhile said Russia will continue to seek a mutually acceptable solution — what he called a “hikiwake” or a “draw” using judo terminology — in negotiations for a peace treaty with Japan. Putin is a well-known enthusiast of the sport.

Also Thursday, the foreign ministers of Japan and Russia restarted stalled talks for resolving a long-standing territorial dispute that has been a sticking point in efforts to sign a postwar peace treaty.

Toshimitsu Motegi, who is visiting Russia for the first time since taking the post in September, said he had a “substantive discussion” with his counterpart, Sergey Lavrov, on how to go about settling their differences.

“We will continue discussions, sorting the issues that need to be tackled so we can reach a mutually acceptable solution,” he said at a joint news conference.

The two agreed to start working-level talks in mid-January to advance plans to conduct joint economic activities in the Russia-held disputed islands off Hokkaido.

But the meeting was somewhat overshadowed by the detainment of five Japanese fishing boats by Russian border patrol authorities earlier in the week that were suspected of violating catch quotas around the islands.

Motegi said he called on Russia to release the boats and their crews from a “humanitarian perspective,” while Lavrov urged Japan to comply with a bilateral agreement on fishing around the islands, called the Northern Territories by Tokyo and the Southern Kurils by Moscow.

Lavrov also said the countries will conduct a joint anti-piracy exercise off Somalia in the Gulf of Aden near the end of the year.

Prime Minister Shinzo Abe had hoped during talks with Putin in June to secure the return of two of the four islands, based on a 1956 joint declaration.

But leading up to the meeting, Putin ramped up criticism of the Japan-U.S. security alliance and took a more hard-line approach, forcing Abe to seek an alternative route toward an agreement.

Japan has since shifted its focus to the joint economic projects, which Russia hopes will boost the economy of its underdeveloped Far East. The projects cover five fields — aquaculture, greenhouse farming, tourism, wind power and waste reduction — with some programs expected to start in earnest next year.

The dispute over the sovereignty of the islands has remained a major stumbling block to the countries signing a formal peace treaty more than 70 years after the end of World War II.

Tokyo claims the Soviet Union seized the islands illegally soon after its surrender, while Moscow argues it did so legitimately.

Motegi and Lavrov have previously met twice in their capacity as lead negotiators, most recently last month in Nagoya. But both encounters were relatively short, and Motegi has said Thursday’s meeting will be the starting point for in-depth discussions.

Motegi is on a five-day day trip to Russia, having met with Economic Development Minister Maxim Oreshkin on Wednesday to discuss economic cooperation. He returns to Japan on Saturday.