Chinese ships enter disputed waters: Japan coastguard

File photo of a Chinese coastguard ship.

TOKYO - Three Chinese coastguard ships sailed into disputed waters in the East China Sea Friday as Beijing maintained its defiant stance after US President Barack Obama backed Tokyo in the row.

The Japanese coastguard said the Chinese vessels entered the 12-nautical-mile band of territorial waters around one of the Senkaku islands, which China also claims and calls the Diaoyus, shortly before noon (0300 GMT).

It was the third such incursion since US President Barack Obama vigorously reasserted on April 24 that Washington would defend Japan under a bilateral military treaty if China initiated an attack in the tense dispute.

China has already dismissed Obama's position, saying that the islands are "China's inherent territory".

Chinese vessels and aircraft regularly approach the East China Sea archipelago - thought to harbour natural resources - after Japan nationalised some of the islands in September 2012, setting off the latest spate of incidents in a long-running territorial dispute.

Relations between Tokyo and Beijing have fallen to their lowest point for years.