(CNN) A US Navy P-8A Poseidon reconnaissance plane flew over the Taiwan Strait on Friday in a demonstration of the United States' "commitment to a free and open Indo-Pacific," just days after dozens of Chinese warplanes entered Taiwan's self-declared air defense identification zone, US Indo-Pacific Command said in a statement.
"A U.S. Navy P-8A Poseidon transited the Taiwan Strait in international airspace on June 24. The United States will continue to fly, sail and operate anywhere international law allows including within the Taiwan Strait," the statement read.
"By operating within the Taiwan Strait in accordance with international law, the United States upholds the navigational rights and freedoms of all nations. The aircraft's transit of the Taiwan Strait demonstrates the United States' commitment to a free and open Indo-Pacific."
In response, the People's Liberation Army (PLA) Eastern Theater Command mobilized air and ground forces to monitor and guard the entire operation of the US aircraft, according to a Chinese military account on social media platform Weibo.
"We express firm opposition to the US' deliberate act to disrupt the regional situation and undermine peace and stability across the Taiwan Strait," said the Weibo post, adding that troops were on "high alert at all times to resolutely safeguard national sovereignty."
The US flyover came after China sent 29 planes into Taiwan's self-declared air defense identification zone (ADIZ) -- the third-highest daily number since the start of the year, and less than a month after China sent 30 warplanes on a similar mission.
The 29 planes were a mix of fighter jets, early warning and control aircraft, electronic warfare aircraft, anti-submarine aircraft, electronic intelligence aircraft, and aerial refueling aircraft, said the Chinese Defense Ministry on Tuesday.
The issue of Taiwan has been at the forefront of US-China relations in recent months.
Tensions between Washington, which is committed to supporting the island's self-defense, and Beijing over Taiwan were in the open earlier this month when their respective defense chiefs met at the Shangri-La Dialogue defense conference in Singapore.
Taiwan and mainland China have been governed separately since the defeated Nationalists retreated to the island at the end of the Chinese civil war more than 70 years ago.
But China's ruling Chinese Communist Party (CCP) views the self-ruled island as part of its territory -- despite having never controlled it.
Beijing has not ruled out military force to take Taiwan and has kept pressure on the democratic island over the past few years with frequent warplane flights into the island's ADIZ.
An ADIZ is unilaterally imposed and distinct from sovereign airspace, which is defined under international law as extending 12 nautical miles from a territory's shoreline.
The US Federal Aviation Administration defines it as "a designated area of airspace over land or water within which a country requires the immediate and positive identification, location and air traffic control of aircraft in the interest of the country's national security."
In a keynote speech in Singapore, Chinese Defense Minister Wei Fenghe accused the United States of being a "bully" in the region and vowed the PLA would "fight to the very end" to stop Taiwanese independence.
After the Shangri-La conference, China's Foreign Ministry reasserted previous statements that the Taiwan Strait "is not international waters."
"The waters of the Taiwan Strait extend from the coasts on both sides of the Strait to the centerline of the Strait, and are China's internal waters, territorial sea, contiguous zone and exclusive economic zone in that order," Foreign Ministry spokesman Wang Wenbin said in a briefing on June 13, citing the United Nations Convention on the Law of the Sea and China's domestic law.
Reiterating Beijing's stance on Wednesday, an editorial in China's state-run tabloid Global Times claimed that the entire Taiwan Strait -- the 110-mile-wide (180 kilometers) body of water between Taiwan and mainland China -- is not international waters, but rather completely under Beijing's jurisdiction.
The actions of US and foreign warships that regularly pass through the strait constitute provocations that violate Chinese sovereignty and are not innocent passage, a recognized international right, the Global Times said.
The US Navy sees things differently, regularly sending warships through the strait, including on May 10, when the guided missile cruiser USS Port Royal made a transit.
Similarly to airspace, international law stipulates that a country's territorial waters extend 12 nautical miles from its coastline.