Taiwan's coast guard says the man who was arrested on Sunday for illegally entering a harbor in northern Taiwan on a small boat is a former Chinese military officer.

At a news conference on Tuesday, coast guard officials said the man is a former Chinese navy officer.

He had sailed a speedboat into a harbor at the mouth of the Tamsui River leading into Taipei. The river mouth is about 20 kilometers from central Taipei where the presidential office is located and is regarded as a key area in terms of security.

The officials said they detected the boat on radar as it approached the shore but misjudged it as a Taiwanese fishing boat, and failed to take action even after realizing it was not Taiwanese.

The coast guard says it has decided to punish 10 officials in charge of monitoring the area.

Analysts say China may have used so-called grey zone warfare, without resorting to open combat, in order to test Taiwan's ability to respond to incidents.

Taiwan's authorities say they will reconsider security measures, including reinforcement of personnel and equipment.