Japan has been formally classified for the first time since World War II as an aircraft-carrier power by a leading Western international affairs think tank.

Japan has one Hyuga-class aircraft carrier, according to Military Balance 2011, an annual report published on Tuesday by the London-based International Institute for Strategic Studies (IISS) assessing the military capabilities and defense economics of 170 countries worldwide.

The annual report is an essential resource for those involved in security policymaking, analysis and research.

Classifying Japan as an aircraft carrier power means China now has four Asian neighbors with the giant vessel. Russia, India and Thailand are reported to have one aircraft carrier in service.

Former Japanese foreign minister Seiji Maehara, shortly before he resigned for accepting an illegal donation, expressed Japan's "grave concern" over China's military development and alleged plan to build an aircraft carrier.

Gary Li, an expert on Asia military affairs at the IISS and the chief researcher of the East Asia section of Military Balance 2011, said Japan currently had one Hyuga and another is under construction.

"The Hyuga is not yet as powerful as the Japanese Maritime Self-Defense Force (JMSDF) would like it to be, mainly because there are no F-35s (fighter jets) as yet," Li said.

"Once Japan acquires F-35s or another suitable short take-off aircraft for the Hyuga class, it will have a greatly increased expeditionary capability, and can operate in conjunction with the US more and more in regional security operations."

Li said the JMSDF is "very powerful" in terms of capabilities. "Its assets are arguably the second best after the US. The ships are modern, powerful, and with a wide range of services. However they suffer from the same problems as the Chinese navy in that it lacks expeditionary capabilities and also the crew lack real battle experience."

Despite Japan's concern over China's military development, Christian Le Miere, research fellow for Naval Forces and Maritime Security at the IISS, said Japanese naval power is superior to China's.

He said Beijing's "main strategy" is still to "deter or prevent US intervention into Taiwan contingency for as long as possible".

In fact, long before the IISS classified only one Hyuga-class vessel as an aircraft carrier, earlier reports said Japan launched the second of the vessels, the Ise, as early as 2009.

The 197-meter long, 13,950-ton vessel can carry up to 11 helicopters.

The vessel is scheduled to be commissioned into the JMSDF this month, Xinhua News Agency reported in 2009.