Britain says it is deploying its flagship aircraft carrier to the South China Sea, with British and US F-35 fighter jets aboard, in the UK's biggest mission yet to the region.

It escalates a tense situation, as China fiercely asserts that the sea is its territory and frames other naval vessels' sailing there as an assault on its rights.

Britain and the US have been conducting naval exercises in the region for years, which often provoke angry responses from Beijing.

Last summer, Britain sailed the HMS Albion, an amphibious assault ship, through the contested waterway. The HMS Queen Elizabeth would be the UK's first aircraft carrier to be sent, a significant upgrade.

Britain has announced plans to send its new aircraft carrier to the South China Sea, intensifying an already tense stand-off with China over who controls the waterway.

UK Defense Secretary Gavin Williamson announced the deployment of the carrier, the HMS Queen Elizabeth, in a speech Monday morning.

The mission, announced at the Royal United Services Institute think tank in London, marks the most significant deployment yet of Royal Navy assets to the South China Sea.

In August, China criticized what it called the "provocative actions" of the HMS Albion, which sailed close to the disputed Paracel Islands in the South China Sea, which China says are its territory.

The Queen Elizabeth's mission is likely to provoke a similar response.

The HMS Queen Elizabeth arriving in New York on October 19. Getty

Williamson said that Royal Air Force F-35 fighter jets would be aboard the Queen Elizabeth, along with F-35s from the US military.

The Queen Elizabeth, which cost some $4.5 billion, recently qualified for full-fledged service after completing training with F-35B jets near Naval Air Station Patuxent River in Maryland in September.

After conducting the South China Sea mission, Williamson said the Queen Elizabeth would move on to the Mediterranean and the Middle East.

—HMS Queen Elizabeth (@HMSQNLZ) February 11, 2019

Both the US and UK navies have had close calls with China in the South China Sea.

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One US destroyer, on a freedom-of-navigation exercise in October, sailed close to Chinese-occupied territory and passed a Chinese destroyer as close as 45 feet.

The US and the UK conducted their first join maneuvers in the region since 2010 on January 11, when the Royal Navy frigate Argyll joined the US Navy Arleigh Burke-class guided-missile destroyer McCampbell on a communications drill.

China claims that the South China Sea is its territory. Neighboring Brunei, Malaysia, Indonesia, the Philippines and Vietnam have rival claims over it.

Read more: China moves 'ship killer' missiles into firing range as US warships infuriate Beijing in the South China Sea

The sea is a vital and busy trade route — about $3 trillion of ship-borne trade passes through the area every year.

The aircraft carrier Nimitz, the guided-missile cruiser Chosin, the guided-missile destroyers Sampson and Pinkney, and the guided-missile frigate Rentz operating in formation in the South China Sea. US Navy

The same day as Williamson made the announcement, the US destroyers Spruance and Preble sailed close to the Spratly Islands, which was condemned by China.

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Chinese state media cited a government representative saying the mission "undermined the peace, security, and order" of the region.