Japan has issued a protest to Beijing after China installed radar equipment in a gas exploration platform near the disputed waters in the East China Sea, a Japanese foreign ministry spokesperson said on Sunday.

The radar that has been installed is commonly found on patrol ships and it is not necessary for gas field development.

The Japanese media reported that the nation is scared that the radar could be a sign of China's intentions to use the gas exploration platforms as military stations in the conflicted zone.

The spokesperson said Japan discovered the radar in late June and filed a protest on Friday through its embassy in China. Japan urged Beijing to explain the purpose of such installations.

In 2008, both the countries had a mutual agreement to maintain cooperation on resources development in the area but no official border was drawn between them.

However, Japan has been accusing China of unilateral developments despite the agreement. Japan said it has been calling on Beijing to halt the construction of its oil-and-gas exploration platforms in the disputed East China Sea.

Japan issued another protest to China on Saturday regarding the Chinese coastguard ships and about 230 fishing vessels which were seen sailing close to Japan's territorial waters around disputed islets in the East China Sea.