Taiwan scrambled jets Wednesday as China's sole aircraft carrier led Chinese warships through the Taiwan Strait with all eyes on Russia, a U.S. defense official confirmed to Fox News.

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It was the second time China sailed the aircraft carrier, the Liaoning, through the strait in the past few weeks, with tensions between Beijing and Taiwan escalating. The carrier was traveling northwest along the center line dividing the strait, along with its battle group.

It came a few days after China flew another nuclear-capable H-6 bomber down to a set of contested islands in a show of force. The bomber flew around the Spratly Islands on Sunday.

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Taiwan's military was closely monitoring the ships' passage and urged the public not to be alarmed. Taiwan regularly dispatches planes and ships to keep a watchful eye on Chinese forces' movements around the island, although the military gave no details about its specific response.

The heavily trafficked 100-mile-wide Taiwan Strait separates Taiwan from southeastern China. The carrier was on its way back from its first journey to the Western Pacific, where it carried out a training exercise, Reuters reported.

Based on a Soviet-built platform and commissioned in 2012, the Liaoning earlier this month carried out what Beijing called routine combat drills in the South China Sea. China has fortified the area with seven man-made islands, some containing runways and coastal defenses.

China declared in November that the carrier and its complement of J-15 fighter jets were combat-ready, setting off jitters in an already tense region.

The Liaoning set off for the Western Pacific last month, passing through the Miyako Strait, south of Okinawa, and then the Bashi Channel separating Taiwan from the Philippines as it entered the South China Sea.

Japanese and Taiwanese surveillance aircraft and ships closely monitored the Liaoning along its journey, seen by some as a sign of how China plans to use the carrier to demonstrate its willingness to back up its territorial claims with military muscle.

China and Taiwan split amid civil war in 1949 and Beijing has never renounced its threat to use force if it considers that necessary to prevent the island's permanent independence from the mainland.

Relations between the sides have deteriorated badly since Taiwanese elected independence-leaning President Tsai Ing-wen last year, and Chinese officials have warned of more turbulence ahead unless she endorses Beijing's view that Taiwan is part of China.

China has been steadily ratcheting-up the economic and political pressure on Tsai, discouraging Chinese tourists from visiting the island of 23 million and intervening to prevent its participation in international forums. That has fueled speculation that Beijing will seek to win away more of the island's dwindling number of diplomatic allies, which now stand at just 21.

"Looking ahead in 2017, the development of cross-strait relations faces increased levels of uncertainty and the challenge of risk has risen," Ma Xiaoguang, spokesman for the Cabinet's Taiwan Affairs Office, told reporters at a bi-weekly briefing on Wednesday.

Ma said he had no information on the Liaoning's passage through the Taiwan Strait and referred questions on the matter to the Defense Ministry, which did not immediately respond.

Having been thoroughly overhauled in China, the Liaoning represents a new degree of sophistication in the Chinese armed forces that includes ballistic missile submarines and prototype stealth fighters.

China announced in 2015 that it was building additional carriers entirely with domestic technology.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.