Japan has summoned the Chinese ambassador to protest the presence of government ships near contested islands, as a simmering territorial dispute continues to hamper relations between the two Asian powers.

Tokyo's foreign ministry lodged a “strong protest” against China on Tuesday during a meeting between senior diplomatic officials, and demanded that Beijing stop sending vessels to the Japan-administered islands.

Japan says four Chinese maritime surveillance ships entered the area around the resource-rich archipelago on Monday and remained there for 13 hours. Chief Cabinet Secretary Yoshihide Suga called the move “extremely unusual” and “regrettable.”

In recent months, China has repeatedly sent ships to the disputed waters in what some analysts say is Beijing's attempt to establish the fact that it can come and go as it pleases.

China was angered after Japan purchased the islands from a private Japanese landowner in September.

The dispute has escalated in recent weeks, since China began sending marine surveillance planes near the islands, prompting Japan to respond by dispatching fighter jets.

The islands, known in Japan as Senkaku and in China as Diaoyu, are surrounded by rich fishing grounds and potential energy deposits. They have a long history of causing strained relations between China and Japan.

Japan says it discovered the uninhabited islands in the late 19th century. China disputes the claim, saying ancient maps show the islands have been claimed by Beijing since the 14th century.