TOKYO — Japan has summoned China's envoy to protest what Japanese authorities consider actions by Beijing's forces that threaten to escalate tensions over disputed remote islands.

The Japanese Foreign Ministry summoned Chinese ambassador Cheng Yonghua to complain about two recent incidents Tokyo considers provocative.

Defense Ministry officials say a Chinese (Jiangwei-2 class) frigate directed weapons-related fire-control radar last Wednesday at a Japanese maritime-self-defense-force vessel. They say a similar incident (involving a Jiangwei-1 class frigate) occurred on January 19th and targeted a Japanese military helicopter.

Japanese Defense Minister Itsunori Onodera says the radar locked on the ship for some time, from a distance of three kilometers, on January 30th.

The defense minister tells reporters this extremely unusual action could have resulted in a dangerous incident.

Japan says the radar the Chinese ship used is normally for guiding missiles.

Tensions have been increasing in the East China Sea over a group of uninhabited islands, the largest of which encompasses barely four-square kilometers. In recent months, China and Japan scrambled fighter jets and have had their maritime patrols closely monitor each other.

The islands, held by Japan, are known as Senkaku in Japanese and Diaoyu in Chinese.

Japan issued a separate protest Tuesday complaining about the latest incursion by Chinese ships into its waters.

Japanese media reports say Deputy Foreign Minister Akitaka Saiki told the summoned Chinese envoy the intrusions “totally counter” expectations for improved relations between the two countries.

Chief Cabinet Secretary Yoshihide Suga told reporters the presence of the maritime-surveillance ships is “extremely regrettable and totally unacceptable.”

China’s Foreign Ministry responded that its ships are on official duty, conducting regular patrols in waters around islands that are Chinese.

Japan’s government has announced it plans to boost its defense budget for the first time in more than a decade and give its Coast Guard additional ships and personnel.