Japan has lodged a protest with Pyongyang after one of its patrol vessels was chased by an apparently armed fishing boat believed to be from North Korea, the government said Thursday.

The incident occurred Friday in the Sea of Japan (East Sea) and within Japan's exclusive economic zone (EEZ), which extends 200 nautical miles from the coast, Tokyo said.

The crew pointed a gun at the Japanese fisheries vessel, forcing it to withdraw, Chief Cabinet Secretary Yoshihide Suga told a news conference.

"The patrol ship suffered no damage as it urgently left the area for safety," Suga added.

Suga said that Japan determined the boat was North Korean by observing and analyzing its crew members as well as other details.

The chief cabinet secretary refused to discuss the North Korean boat's activity or intentions except to say that it was operating illegally. Kyodo News service said the boat was allegedly fishing squid illegally and that it chased the Japanese vessel for more than 10 minutes.

The area is known as rich fishing grounds and Japanese authorities have been patrolling it for illegal operations.

Japan's protest was lodged via North Korea's embassy in Beijing.

Japan and North Korea do not have diplomatic relations but Tokyo sometimes makes diplomatic protests to Pyongyang by having its embassy in the Chinese capital contact North Korea's.