BEIJING â€” China says ships from its newly formed coast guard confronted Japanese patrol vessels Friday in waters surrounding East China Sea islands claimed by both sides.

The State Oceanic Administration that oversees the service says four of its ships "sternly declared" China's sovereignty over the islands called Senkaku by Japan and Diaoyu by China, and demanded they leave the area. The uninhabited archipelago is controlled by Tokyo but also claimed by Beijing.

It was not clear if any action resulted from the Chinese declaration. Such sovereignty declarations are usually made by hailing Japanese boats by radio and loudspeaker, as well as flashing shipboard signs.

Ships from Chinese civilian agencies have maintained a steady presence in the area since tensions spiked in September following Japan's purchase of some of the islands from their private owners.

Those vessels are being replaced by ships from the coast guard, which was formally inaugurated on Monday and merges the resources of four former agencies. China says the move was intended to boost its ability to enforce its maritime claims, upping the stakes in an increasingly tense competition for marine territory and resources in waters off its eastern and southeastern coasts.

Chinese coast guard ships have also been spotted this week 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 protests from rival claimant Manila.

China says virtually the entire South China Sea and its islands belong to it, a claim based on alleged historical precedents that are strongly contested by the Philippines, Vietnam and others.

While Beijing has mainly used civilian agencies to patrol its claims, the new coast guard gives it greater latitude to do so by centralizing operations in a single body. The body is nominally under civilian control, but closely coordinates with the increasingly formidable Chinese navy that recently added an aircraft carrier to its fleet.

Coast guard ships are mainly repurposed naval or commercial vessels and are equipped with light armaments such as machine guns and deck cannons, unlike in the past when most of China's patrol craft had no weaponry.

Japan has already expressed renewed unease about China's military and maritime activity near the disputed islands, and on Friday released a defense paper calling for an increase in its surveillance capability, possibly including the use of drones capable of wide-range, high-altitude monitoring around the clock.

The paper also proposed creating a marine force to defend the disputed East China Sea islands.

Japan scrambled jets on Wednesday to keep watch on a Chinese Y-8 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.

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

Around the same time the Chinese fighter jet was sighted, Japan's coast guard reported the appearance of the four coast guard vessels near the disputed islands.

Japan's coast guard said the four Chinese craft were seen early Wednesday just outside Japanese territorial waters.