Taipei  - Taiwan Tuesday expressed grave concern over the Japanese coast guard vessel's collision with a Taiwanese fishing boat which resulted in the sinking of the boat in the highly-disputed Diaoyu Islands in the East China Sea.

"We have summoned the Japan's representative stationed in Taiwan to assert our sovereignty claim over the Diaoyu Islands and express our deep regret over the incident," Taiwan's foreign ministry said in a statement.

Taiwan and Japan do not have official relations.

The Taiwanese boat, hired by anglers for sea angling within Taiwanese waters, was reportedly chased by the Japanese coast guard vessel when it sailed into waters 10 kilometers south of Diaoyu, called the Senkaku islands by the Japanese, Monday.

Japan had already handed over to a Taiwanese coast gaurd vessel the 13 anglers the Japanese coastguard saved after the boat sank as a result of the collision.

The three crewmen also saved were being held as part of the investigation. The Taiwanese ministry demanded that Japan treat the three crewmen properly and send them back as soon as possible.

The ministry said both the Japanese and Taiwanese sides would launch separate probes into the incident to find out which party was responsible. (dpa)