Tokyo: Japan has lodged a protest with Russia after scrambling four jet fighters to intercept a foreign aircraft believed to be Russian which briefly violated its airspace, officials said Wednesday.
The foreign ministry made the protest shortly after the plane entered Japanese airspace off the northernmost main island of Hokkaido, near a disputed island chain, on Tuesday afternoon.
"We made the protest through the Russian embassy in Tokyo," a foreign ministry official told AFP.
"The Russian side did not confirm the case, only saying they will check facts."
The Japanese Air Self-Defense Force scrambled four jets to head off the intruder, which it believed was Russian after analysing its course, a defence ministry official said.
If confirmed, this would be the first time Russian planes have entered Japanese airspace since August 2013, when two Tu-95 Russian strategic bombers were intercepted off the southwestern island of Okinoshima, the ministry said.
Sixteen seconds after entering Japanese airspace on Tuesday, the plane left towards the Kuril island chain, claimed by Tokyo but controlled by Russia, the ministry added.
Soviet troops seized the islands, known as the Northern Territories in Japan, just after Japan surrendered in World War II.
The seven-decade-old dispute has hampered trade and prevented Moscow and Tokyo from signing a formal peace treaty.
A map on the defence ministry's website showed the plane crossed a halfway line between Japan's Nemuro peninsula and one of the four disputed islands, called Kunashir in Russia and Kunashiri in Japan.
Foreign Minister Fumio Kishida is considering visiting Moscow next week to discuss a possible visit by Russian President Vladimir Putin to Tokyo later this year, the daily Sankei Shimbun newspaper reported.
Kishida's planned visit to Moscow was rescheduled in August after Tokyo hit out at Russian Prime Minister Dmitry Medvedev's trip to one of the disputed islands.
Japan scrambles jets hundreds of times a year to defend its airspace, both against Russia and these days also against Chinese aircraft.
Tokyo scrambled fighters 464 times in the year through March against Chinese aircraft -- a record -- after they breached its air defence identification zones, which cover a wider aerial circle than airspace.
It also sent out military jets 473 times against Russia over the same period.
Beijing has warned this is heightening tensions between the two Asian powerhouses, which are already at loggerheads over a longstanding territorial conflict in the East China Sea and Japanese military aggression in the first half of the 20th century.
"While actual incursions are increasing amid the recent uncertainty, the Self-Defence Forces also appear to want to display their presence in the region," said Hisao Iwashima, a defence analyst.