Russian airplanes flew in the region of a joint US-Japanese military drill, a naval spokesman said on Wednesday, heightening tensions in a territorial dispute between Tokyo and Moscow.

USNS Tippecanoe (C) refuels Japan Maritime Self Defence Force destroyers Ikazuchi (R) and Kongo during their military manoeuvres known as Keen Sword 2011, in the Pacific Ocean Dec 5, 2010. US and Japanese forces began military manoeuvres last Friday.[Photo/Agencies]

"The area is our zone of responsibility. The airplanes carried out a planned flight in an area of the Russian Pacific Fleet's regular activity," said Roman Markov, a spokesman for the fleet.

"Our pilots did not violate any rules of international air space," he said.

Japan's Sankei newspaper had earlier reported that Russian patrol planes had interrupted joint US and Japanese military drills this week when they entered airspace above where the exercises were being conducted in the Sea of Japan.

Markov said that two Ilyushin-38 airplanes -- a maritime patrol and an anti-submarine aircraft -- had made the flights.

Ties between Japan and Russia have been strained since Russian President Dmitry Medvedev infuriated Tokyo last month by becoming the first Russian leader to visit one of a string of islands claimed by both countries.

His trip to the islands -- called the Southern Kuriles in Russia and the Northern Territories in Japan -- caused Tokyo to recall its ambassador for consultations.