This month, China released a defense white paper that, among other things, reiterated that Beijing would not renounce the use of force to achieve reunification with Taiwan.

Around the same time as the paper was released, China's J-20 stealth fighter was officially deployed to the country's Eastern Theater Command, which encompasses Taiwain.

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China's J-20 stealth fighter has been officially deployed to the country's Eastern Theatre Command, suggesting it will be focused on the Taiwan Strait and military activities between Japan and the United States, observers said.

The People's Liberation Army Air Force posted a photo on its social media account this week showing the fifth-generation fighter tagged with the number 62001, designating the aircraft as part of a frontline unit.

Chinese media reported that the stealth fighter had entered the Eastern Theatre Command, which encompasses Taiwan.

Collin Koh, a research fellow at the S Rajaratnam School of International Studies at Nanyang Technological University in Singapore, said the aircraft appeared to have two missions.

"The unit turning operational in Eastern Theatre Command is precisely aimed at Taiwan," Koh said. "And to challenge US military activities in Taiwan Strait, besides posing a threat to the median line that Taiwan's air force patrols along."

The photo's release came as China issued a defence white paper, highlighting the risks from "separatist forces."

In the document, the military said it faced challenges from pro-independence forces in Taiwan but would always defeat those fighting for the island's independence. It also said there were risks from separatists in the autonomous regions of Tibet and Xinjiang.

A day after the paper was released, an American warship sailed through the Taiwan Strait.

The J-20 is expected to enter mass production this year. If the aircraft was declared ready to go into active operations, it would signal China was a "greater threat" and had "greater capability" in the Pacific, Gen. Charles Brown, the US Air Force's Pacific commander, said in May.

Brown said US efforts to counter those developments included increasing deployments of next-generation F-35 jets and continuing overflights of strategic areas such as the South China Sea.