The Japanese Air Force has been repeatedly tested since April, with fighter jets being sent to monitor unidentified aircraft approaching Japanese airspace no fewer than 340 times in the space of twelve weeks.

Embroiled in territorial disputes with all its immediate neighbors, Japan encountered Russian aircraft on 235 occasions, up from 204 year on year. Of the remainder, the vast majority turned out to be Chinese military aircraft operating in the air-defense zone which Beijing unilaterally declared over a vast area of the East China Sea in November of last year, but which both Japan and the United States dispute.

Analysts say the heightened activity by Chinese and Russian forces underlines the instability in the region. "The two countries have different agendas at the moment," said Tomohito Shinoda, a professor at The International University of Japan, in Niigata Prefecture. "For the Russians, this increase in flights can be seen as a message to the Americans at a time when Moscow and Washington have been at odds over the situation in Ukraine and the Crimea," he said.

Monitoring US forces

"The Russian air force probably wants to make sure that the Americans are not planning to do anything from their bases in Japan, such as in Aomori," he said. "I also think it is likely that the Russian air force wants to show that it is still a relevant regional player," he added. "Some of these flights could be considered provocative and they were not needed."

It therefore seems that the Russian aircraft are testing Japan's air defenses and response times in the very far north of the Japanese archipelago. A recent Defense White Paper confirmed an increase in flights by Russian long-range Tu-95MS bombers that can be refueled in flight and that there are an estimated 570 combat aircraft in Russia's Far East forces.

Many of the Russian aircraft that were tracked by the Japanese military were long-range reconnaissance and electronic eavesdropping planes. The rise in scrambles also coincided with the US and South Korea carrying out joint military exercises, involving air and naval assets, in the Sea of Japan between late February and mid-April.

Washington deployed a dozen state-of-the-art F-22 stealth fighters in Okinawa in January, while the Pentagon also announced that the aircraft-carrier USS Ronald Reagan will be based at the Yokosuka Naval Base, south of Tokyo, from the latter part of 2015.

'Pacific pivot'

The two transfers are part of the broader reallocation of Washington's defense assets throughout the Asia-Pacific region, a policy that has been described as the "Pacific pivot." The focus of that pivot is unquestionably China, which has been rapidly upgrading its military capabilities and is not reluctant to push its territorial claims with a degree of force.

As well as disputing the sovereignty of the Senkaku/Diaoyu Islands with Tokyo, Beijing is locked in a confrontation with Vietnam and the Philippines over isolated shoals and islands in the South China Sea.

Russia and China also carried out their first-ever joint naval drills in April and vowed to carry out more in the future. Analysts suggest the Chinese were particularly keen to stage the maneuvers as they would serve as "a clear statement by the Chinese that they now have an ally in the region."

Russian deterrence

"It also benefits Russia as it can intensify its activities in the skies around Japan," a military analyst for the Japanese government told DW. "Russia has to increase and enhance its strategic deterrence capabilities," he said. "And because Japan supported the US on the Crimea issue, then there have been some bilateral difficulties between Tokyo and Moscow, but I think it is quite clear that Prime Minister [Shinzo] Abe wants to improve relations with Russia."

The two most critical issues for Moscow and Tokyo are an alliance that can serve as a bulwark against the aggressive Chinese expansionism that both governments fear. In addition, there is also the future of a number of islands off the most northerly Japanese island of Hokkaido that were seized by the Soviet Union in the final days of World War II.

Tokyo refers to the isles as the Northern Territories but Moscow knows as the Southern Kurile Islands.

Japan and Russia have held sporadic discussions on the future of the four islands and last year it appeared that a breakthrough was close. The agreement would see the uninhabited islands returned to Japan and the others being jointly developed by both nations. That tentative deal was jeopardized by the international reaction to the crisis in the Ukraine earlier this year.

"I think Mr Abe has a good personal and working relationship with [Russian President] Vladimir Putin, but the Crimea situation has been an obstacle to more progress in bilateral ties," Professor Shinoda said. "But I think that the relationship can be revived in the future. And Abe has plenty of time to make progress on this issue."