China strongly decried on Monday the "illegal" intrusion of a US warship into waters it claims in the South China Sea shortly after the US Navy said its guided-missile destroyer the USS Milius had "sailed through the area."

Earlier, the US Navy said in a statement that "this freedom of navigation operation upheld the rights, freedoms, and lawful uses of the sea," stressing that the ship passed near the Spratly Islands.

"Missile destroyer USS Milius illegally intruded into the waters adjacent to the Meiji Reef in China's Nansha Islands without the approval of the Chinese government," Tian Junli, spokesperson for the Chinese military's Southern Theatre Command, said in a statement, adding Beijing's air force "followed and carried out surveillance of the vessel."

Concurrently, Beijing said fighter jets carrying "live ammunition" had conducted "simulated strikes" near Taiwan and that its Shandong aircraft carrier was involved in the ongoing drills.

Commenting on this issue, Japan's joint staff said it had detected the Shandong and several other Chinese naval vessels in the area south of Miyako island since Friday.

"We confirmed approximately 120 landings and departures on the Chinese navy's Kuznetsov-class aircraft carrier Shandong, 80 times by fighter aircraft and 40 times by helicopters," the statement added.

Japanese forces mobilized two escort groups to surveil the Chinese vessels and "Air Self-Defense Force fighter jets scrambled in response to the landing and take-off of the fighter jets on board" the Shandong, the statement revealed.

It is worth noting that Shandong's activity in the Pacific Ocean was officially confirmed by the Japanese defense ministry for the first time by direct observation.

This is happening as Beijing's war drills entered their third day. 

The big picture

China launched Saturday military drills around Taiwan in a stern warning to the Taiwanese government following a meeting between the island's leader and the US House speaker.

Operation United Sharp Sword is set to last for three days, running until Monday, Chinese media reported. It will include rehearsals on an encirclement of the Island off the coast of China, the People's Liberation Army's Eastern Theater Command revealed.

The military drills were swiftly denounced by Taiwanese President Tsai Ing-wen Tsai, who pledged to work with "the US and other like-minded countries" against "continued authoritarian expansionism."

China's drills will see Beijing sending planes, ships, and personnel into "the maritime areas and air space of the Taiwan Strait, off the northern and southern coasts of the island, and to the island's east," Shi Yin, a PLA spokesperson said.

This comes amid a period of tension with China heightened by a meeting between Tsai and US House Speaker Kevin McCarthy, during a stopover by the Taiwan leader in the United States.

McCarthy was planning on visiting Taipei himself rather than receiving Tsai in California. But the decision to change the plan came to allegedly avoid escalation with China.

Tsai, who was on an official visit to Latin America, made two stopovers in the US during which she met with house speaker McCarthy and other legislators.

The announcement regarding the drills comes a day after Chinese warships patrolled near Taiwan for the second consecutive day.

Announcing that Taiwan remains an "inseparable part" of the country, China also sent a fighter jet and an anti-submarine helicopter which "crossed the island's air defense identification zone (ADIZ)," according to the Defense Ministry in Taipei.

Read more: China sees Tsai's US stop 'provocation', US urges no 'overreaction'