Russia and Japan have complex relations marked by decades of 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 Two, 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 militarisation 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 World War Two – a “Day of Victory over Militaristic Japan”, spurring a protest from Tokyo.

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

Japan’s defence ministry on Thursday sought a record US$53 billion in the next fiscal year’s budget, part of its biggest military build-up since World War Two, aiming to double defence spending to 2% of gross domestic product by 2027, citing an increasingly assertive China and an unpredictable North Korea.