Senior Taiwanese officials confirmed on Tuesday that the Chinese man arrested for illegally entering a Taipei harbor in his speedboat is a former naval captain who may have been testing the island's defenses.

The man was arrested by the Taiwanese coast guard on Sunday in the coastal district of Tamsui. His boat had entered a river leading into Taipei. This incident occurred amid ongoing tensions between Taiwanese and Chinese.

China claims that the island, which is democratically run, is its territory. Taipei denies this claim.

Kuan Bi -ling, the head of Taiwan’s Ocean Affairs Council which oversees the coastguard, told journalists at the parliament that the man is "quite refined" and has a good presentation. He had also served in the Chinese navy as a captain.

Kuan stated that there were 18 cases similar to this in the last year, most of which involved Taiwan-controlled islands located near the Chinese coast.

She said that based on the number of cases Taiwan has seen in the past it is impossible to rule out the possibility that this was a test.

Requests for comment were not immediately answered by either the Taiwan Affairs Office or the Ministry of Defence in China.

Taiwan Defence Minister Wellington Koo said, speaking also to reporters in parliament, that the boat incident may be an example of China's grey zone tactics against the island.

Taiwan has complained to China in recent years about the use of so-called gray zone warfare, which is a tactic designed to exhaust an enemy by irregular tactics and without resorting open combat. For example, floating surveillance balloons above the island.

Koo stated that "these grey zone tactics were always in place." We must never lose our vigilance, and we cannot rule out countermeasures.

Two Taiwanese fisherman strayed in Chinese waters in March near the Taiwan controlled Kinmen Islands, which are located next to China's coastline. One of the two, a Taiwanese officer, is still in Chinese custody, while his counterpart was released shortly after. (Reporting and editing by Miral Fahmy; Additional reporting by Roger Tung, Jeanny Kao, and Ben Blanchard)