Tokyo : Tokyo expressed unease Thursday over Chinese military and maritime activity near disputed islands that Japan controls, as China defended a flight by one of its fighter jets near Japanese airspace.Japan had scrambled fighter jets Wednesday to keep watch on a Chinese early warning plane flying over international waters between Japan’s southern Okinawa island and an outer island relatively close to the disputed area in the East China Sea.

Japanese Prime Minister Shinzo Abe expressed concern over the sighting. “It was an unusual action that we have never seen before. We’ll keep monitoring it with great interest,” Abe said Thursday before leaving for a trip that will take him to Malaysia, Singapore and the Philippines.

During his travels, Abe plans to discuss ways to cooperate on maritime security, officials said. “I would like to share an understanding that we need to observe a rule of law, not a rule by force,” Abe said.

The Chinese Defense Ministry issued a statement defending the right of its aircraft to operate in the area.

The training flight was a “scheduled annual arrangement that was not directed at any specific countries or targets and was in accordance with relevant international law and practice,” China’s official Global Times newspaper quoted an unidentified ministry spokesman as saying.

Japanese Defense Minister Itsunori Onodera said late Wednesday that the flight of the Chinese Y-8 early warning plane was “a sign of China’s escalating maritime advance.”

Around the same time the Chinese fighter jet was sighted, Japan’s coast guard reported the appearance of four Chinese coast guard vessels near the disputed islands, for the first time since Beijing revamped the service to improve its ability to enforce its maritime claims.

Japan’s coast guard said the four Chinese craft were seen early Wednesday just outside Japanese territorial waters around the tiny uninhabited islands called Diaoyu by China and Senkaku by Japan. Chinese websites ran photos reportedly taken by the Japanese coast guard showing a ship painted in the service’s new red, white and blue striped Chinese coast guard livery.

Tokyo is considering introducing drones, or unmanned aerial vehicles, like the Global Hawk used by the U.S. military, and beefing up the role of self-defense troops in southwestern Japan to improve its defenses against China’s increased activity, Japanese media reported Thursday. Those plans are expected to be included in an interim defense policy report due for release Friday.

Apart from its claims in the East China Sea, China has sparred with the Philippines and Vietnam over overlapping claims to parts of the South China Sea, another area to which the new Chinese coast guard is being deployed.

A Chinese coast guard ship was sighted recently at Mischief Reef off the western Philippine coast, according to a confidential Philippine government report obtained by The Associated Press. China occupied the vast reef in 1995, sparking fierce protests from rival claimant Manila.

Associated Press writer Jim Gomez in Manila, Philippines, contributed to this report.