China would probably gain air superiority very quickly in an attack on Taiwan after Russia failed to do so in the midst of the Ukraine war, leaked US intelligence documents show, according to reports.

The documents were released as part of the Pentagon Files that came to light over the past few weeks. As early as March 2, 2023, over 100 intelligence papers were posted on Discord, a social media platform popular with gamers.

The documents contained US national security secrets related to China, Ukraine, and the Middle East - including sensitive intelligence reports, Ukraine war plans, and information on allies that the US obtained through spying on them.

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A former US intel source told Politico that the documents contained markings in their corners which suggested that they corresponded to specific wires that were compiled in summary form - a practice is often used by government staffers to prepare briefing packets.

Although the documents don't appear to have been doctored, one of the papers was identified as heavily altered.

Moreover, the documents, allegedly leaked by a US national guardsman, in the worst US security breach in a decade, revealed that the military and defense leaders of Taiwan doubt that their air defenses would be able to "accurately detect missile launches," while only about half of the island's aircraft are capable of effectively engaging hostile targets.

The employee was arrested on Thursday over the leaks, with US Attorney General Merrick Garland saying US law enforcement arrested a military service member as a suspect in connection with a leak of classified defense information online.

"Today, the Justice Department arrested Jack Douglas Teixeira in connection with an investigation into alleged unauthorized removal, retention, and transmission of classified national defense information," Garland said during a press conference.

BREAKING: US intelligence leaker Jack Teixeira, a 21-year-old member of the Air National Guard, is arrested at his home in Massachusetts. pic.twitter.com/vZ2y6d3Fqd

— 301 Military (@301military) April 13, 2023

Taiwan fears it could take up to a week to move its aircraft to shelters, leaving them vulnerable to Chinese missile strikes, the reports claimed.

A report published by Politico on Tuesday revealed that the US had been facing an avalanche of questions from its frustrated allies over the leak of classified Pentagon documents.

The leak had left relations with allies in a state of crisis as the incident is reported to be the largest since Wikileaks exposed classified files from 2006 to 2021.

Other sources told Politico that officials from London, Brussels, Berlin, Dubai, and Kiev requested answers from Washington about the leak. They also asked whether the Biden administration was taking appropriate measures to limit the spread of future intel.

Read more: Leaked documents may have originated in chatroom for gamers: Reports

Moreover, China using civilian shipping, including passenger ferries, for military purposes, has hampered the US intelligence community's ability to predict when China might take military action, The Washington Post reported.

Last week, Taiwan kicked off emergency response drills, enacting numerous scenarios, including missile attacks and chemical weapons.

The Pentagon criticized Taiwan's missile drills as too highly scripted, which could leave their armed forces and leadership unprepared for a "real-world event," WashPo said.

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This comes amid a period of tension with China heightened by a meeting between Taiwanese President Tsai Ing-wen 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.

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.