Tensions have spiked over the last week or so after Taiwan reported multiple Chinese fighters and bombers flying into the zone last weekend, in an area close to the Taiwan-controlled Pratas Islands in the northern part of the South China Sea.

The Chinese missions coincided with a U.S. aircraft carrier group entering the South China Sea for what the U.S. military termed a routine deployment. The United States has criticised the Chinese flights.Taiwan's Defence Ministry said a total of seven Chinese aircraft flew into the same waters near the Pratas Islands on Sunday - two J-10 fighters, four J-11 fighters and a Y-8 reconnaissance aircraft.

It added that a U.S. reconnaissance aircraft was also present in the same southwestern part of the defence zone, but neither named the aircraft type nor provided details of its flight path, which it does for all Chinese flights.

It was the first time Taiwan had mentioned the presence of a U.S. aircraft since it began near daily reports of Chinese activity in its defence zone in mid-September.Taiwan rarely speaks publicly about U.S. activity near it, normally when U.S. warships sail through the Taiwan Strait, though diplomatic and security sources say there are frequent U.S. air and naval missions close to the island.The United States, like most countries, has no official diplomatic ties with Chinese-claimed Taiwan, but is the island's most important international backer and supplier of weapons.

China toughened its language towards Taiwan last week, warning after its stepped up military activities that "independence means war" and that its armed forces were acting in response to provocation and foreign interference.

China believes Taiwan's democratically-elected government is bent on declaring independence, a red line for Beijing. President Tsai Ing-wen says Taiwan is already an independent country called the Republic of China, Taiwan's formal name.