Taiwan organized warships on Saturday night to monitor the movements of a Chinese carrier strike group after Japan spotted it heading towards the western Pacific, the South China Morning Post reported on Sunday.

The fleet – part of China’s People’s Liberation Army (PLA) Navy – was reportedly seen passing through the Miyako Strait near Okinawa, and then turning south, Japan’s Ministry of Defense said. The Miyako Strait is about 200 miles east of the northernmost tip of Taiwan.

Although the precise location or heading of the group – led by China’s first aircraft carrier, the Liaoning – was unknown, the Taiwanese navy ordered ships from the northeastern port of Suao to monitor the situation, Taiwan’s Ministry of National Defense (MND) said.

“We have conducted reconnaissance and monitoring over the sea and air space around Taiwan,” MND spokesman Shih Shun-wen said.

Chinese state media called Saturday’s exercise “routine” and in accordance with international law.

“This is a routine arrangement in accordance with the annual plan and is in line with the international law and conventional practice,” PLA Navy spokesperson Gao Xiucheng told Global Times, a Communist Party propaganda newspaper, on Monday.

Gao added that the Chinese Navy will continue to regularly organize similar training and exercises according to its plan to boost the systematic combat capability of its aircraft carrier groups.

Last Friday, the PLA held military drills featuring warplanes near Taiwan, which Chinese state media referred to at the time as part of “military struggle preparations against the island.” In recent months, Beijing has stepped up its aggression towards Taipei, with the PLA increasing its activities around the independent island. China regards Taipei as a renegade province.

The United States has sent military aircraft to operate near Taiwanese airspace to demonstrate support for the island. The U.S. claims to be allied with Taiwan, although it does not formally recognize the island as a sovereign state.

Taiwan’s defense ministry said that also on Saturday evening, the USS Barry-DDG 52, an Arleigh-Burke class guided-missile destroyer, sailed through the Taiwan Strait, likely in an act of support for Taiwan.

China’s Liaoning was escorted on Saturday by two type 052D guided-missile destroyers, two type 054A guided-missile frigates, and a type 901 combat support ship. The Liaoning is currently the only aircraft carrier active in the western Pacific after the Chinese coronavirus began to spread through the U.S. Navy recently, halting operations on some ships.

The USS Theodore Roosevelt carrier had been deployed in the region but was forced to dock in Guam on April 1 after hundreds of its crew contracted the Chinese coronavirus. The ship’s captain was later fired for publicly disclosing information about the incident. A second U.S. aircraft carrier, the USS Ronald Reagan, is currently docked in Yokosuka, Japan after members of its crew also tested positive for coronavirus.