Japan may station military equipment on islands near an archipelago at the centre of a dispute with China, officials said Wednesday, after a number of airborne near-confrontations.

The defence ministry will ask for money in the next fiscal year to study the idea of putting mobile radars and communication systems on islands near the Japan-controlled Senkakus, which Beijing calls the Diaoyus, a defence spokesman said.

"The study is part of our plan to operate in southwestern islands with flexibility," the spokesman said.

The comment came after reports said Japan is considering permanently stationing F-15 fighter jets on Shimoji, a small island near the Senkakus.

Defence Minister Itsunori Onodera denied that and said Tuesday: "We are studying various options as to how to build a sound security system in our southwestern waters."

The maritime dispute, which has simmered for years, heated up last year when the Japanese government nationalised some of the islands, triggering anger and demonstrations in China.

Observers said the protests had some backing from communist authorities in Beijing, who use nationalism to bolster their claims to legitimacy.

Tokyo's defence ministry has said F-15s were sent airborne to head off Chinese state-owned -- but not military -- planes four times in December, including one occasion when Japanese airspace was breached.

They were also mobilised in January, it said.

On the occasion when Japan says its airspace was breached, the air force did not detect the Chinese aircraft, which had already moved off by the time fighter jets were scrambled.