Japan is considering introducing US spy drones to boost surveillance of its territorial waters near islands in the East China Sea at the centre of a bitter dispute with Beijing, Kyodo News said Monday.

The Japanese defence ministry hopes to introduce the unmanned Global Hawk aircraft by 2015 "in a bid to counter China's growing assertiveness at sea, especially when it comes to the Senkaku Islands", the news agency said, citing unnamed government officials.

Beijing has been sending maritime patrol vessels into waters around the Japanese-controlled islands, which China claims as Diaoyu, since Tokyo nationalised the chain in September.

China is apparently seeking to prove that it can come and go in the area at will, and on Monday three of Beijing's ships were spotted in the waters around the islands, according to Japan's coastguard, in the latest perceived incursion.

An earlier report on Monday said China has transferred two destroyers and nine other former navy vessels to its maritime surveillance fleet.