Japan's "militarization" complicates the situation in the Asia-Pacific region, the deputy chair of the Russian Security Council and former President Dmitry Medvedev said on Sunday.

Russia and Japan have a complex relationship marked by a territorial dispute over a handful of small, Russian-held islands off Hokkaido that Moscow calls the southern Kurils but Japan claims as its Northern Territories.

The dispute over the area, which the Soviet Union seized in the final days of World War II, has prevented Tokyo and Moscow from reaching a peace treaty formally ending hostilities.

"It is regrettable that the Japanese authorities are pursuing a course towards a new militarization of the country," the Russian TASS news agency quoted Medvedev as saying.

"Troop exercises are taking place near the Kuril Islands, which seriously complicates the situation in the Asia-Pacific region."

Japan's Foreign Ministry and Prime Minister's Office could not immediately be reached for comment outside business hours.

Russia decided this year to declare Sept. 3 — the day after Japan's surrender in WWII — a "Day of Victory over Militaristic Japan," spurring a protest from Tokyo.

Medvedev said Japan, with help from the United States, was expanding its military infrastructure and increasing its arms purchases.

Japan's Defense Ministry on Thursday sought a record $53 billion in next fiscal year's budget, part of its biggest military buildup since WWII, aiming to double defense spending to 2% of gross domestic product by 2027, citing an increasingly assertive China and an unpredictable North Korea.