Taipei, Taiwan - Taiwan's Defense Ministry resolutely backed its right to self-defense and released photos on Monday showing its air defense remains on high alert after unprecedented military activity from China.

"We will defend our skies. And we will never give up our beliefs," the ministry posted on Twitter. It said the air defense units are steadfastly maintaining their posts.

The Taiwanese response comes as China concluded on Monday its three-day large-scale military maneuvers near Taiwan in retaliation for Taiwan President Tsai Ing-wen's meeting with the US House of Representatives Speaker Kevin McCarthy, a Republican, last week.

"It is a serious warning about the provocative activities of Taiwan's separatist independence forces and their collusion with foreign forces," Foreign Ministry spokesman Wang Wenbin told the press in Beijing on Monday. He sees the exercises as a "necessary step to protect national sovereignty and territorial integrity."

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The pro-independence forces and the foreign forces working in league with them in the Taiwan Strait are the "greatest threat to peace and stability," he said.

He reiterated that Taiwan is a "purely internal China affair."

Late Monday, the Taiwan Defense Ministry registered 91 fighter jets and 12 ships from the Chinese military within the space of 12 hours. This is a record-high number of Chinese military aircraft entering the airspace surrounding Taiwan in a single day.

Of these, 54 aircraft crossed the median line of the Taiwan Strait and entered Taiwan’s south-western and south-eastern airspace.

After Tsai returned from California to Taipei, China launched three-day military exercises on Saturday. They included simulating several precision strikes on "key targets on the island of Taiwan and surrounding sea areas."

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Taiwan's Foreign Ministry on Monday condemned China's provocation, saying it had obviously challenged international orders and undermined the peace and stability in the Taiwan Strait and the region.

On Monday, the US 7th Fleet said that the Arleigh Burke-class guided-missile destroyer USS Milius asserted navigational rights and freedoms in the South China Sea near the Spratly Islands, consistent with international law.

The US has been committed to Taiwan's defense capabilities since 1979, which has so far mostly meant arms deliveries.