Japan has asked China to refrain from “further straining relations” after a flotilla of Chinese warships was seen steering near Japanese islands on Tuesday, causing a ripple in already troubled waters as Beijing flexes its military muscles.

AFP reports that seven warships – including frigates, a guided missile destroyer, a refueler and two submarine rescue vessels – were spotted near waters deemed as Japan’s territory, at about 200 km from the Senkaku Islands.

Director-general of the Foreign Ministry’s Asian and Ocean Affairs Bureau, Shinsuke Sugiyama, called on Beijing to “take appropriate measures while considering the larger picture of the Japan-China relationship”.

The ships, believed to be returning to China after training in the Pacific, traversed Japan’s contiguous zone, or zones beyond the territorial seas of a nation, as permitted under international law. It was the first time the Chinese navy had used the route, a defense ministry spokesman told AFP.

“They were moving north, from the Pacific Ocean to the East China Sea,” the spokesman said. “They passed through the narrow strait on the way back, and this is the first time we have confirmed that they passed through this gap”.

Japanese Defense Minister Satoshi Morimoto said they are monitoring the Chinese ships’ movements.