Two Navy warships transited the Taiwan Strait on Monday in a show of force in Pentagon efforts to push back against China's expansive claims to control waters near the communist mainland.
Pentagon spokesman Lt. Col. Chris Logan said the guided missile destroyer USS Curtis Wilbur and the guided missile cruiser USS Antietam took part in the passage operation "in accordance with international law."
"The ships' transit through the Taiwan Strait demonstrates the U.S. commitment to a free and open Indo-Pacific," Logan said. "The U.S. Navy will continue to fly, sail, and operate anywhere international law allows."
The passage was the second transit through the 100-mile strait this year and highlights intensified U.S. military operations on both the sea and in the air aimed at challenging Chinese claims to sovereignty over regional international waters near its coasts.
The last strait passage by a U.S. warship took place in July.
China in recent months has been conducting provocative flights of military aircraft around Taiwan in an apparent bid to intimidate the island nation that Beijing regards as a breakaway province.
Taiwan government sources said the number of Chinese military flights near Taiwan has decreased in recent weeks.
In May, Chinese Su-35 fighters and H-6 bombers circumnavigated the island nation.
Earlier this month, a Chinese destroyer nearly collided with the USS Decatur, a guided missile destroyer, in the South China Sea as the Chinese ship tried to force the Dacatur to leave the area that China is claiming as its maritime territory.
The Chinese ship came within 45 yards of the Decatur near the disputed Spratly islands that China has been militarizing in recent months with advanced anti-ship and anti-aircraft missiles.
White House National Security Adviser John Bolton bluntly warned the Chinese to halt provocative naval encounters.
"We will not tolerate threats to American service members," Bolton said. "We're determined to keep international sea lanes open. This is something the Chinese need to understand. Their behavior has been unnecessarily provocative for far too long."
The near-collision followed the imposition of U.S. sanctions last month on a senior Chinese general that sparked a harsh Chinese reaction.
The State Department slapped sanctions on Chinese Lt. Gen. Li Shangfu, a senior member of the Central Military Commission and director of the PLA Equipment Development Department that is in charge of weapons procurement.
The sanctions were issued under a new U.S. law aimed at punishing Russia for its illegal takeover of Ukraine's Crimea. The Chinese general had purchased Su-34 jets and S-400 anti-aircraft systems covered by the U.S. law.
In response, China cut off planned military talks in Beijing, recalled a PLA admiral who was visiting the United States, and canceled a planned port call in Hong Kong by a U.S. warship.
The Chinese also responded to the sanctions with the provocative incident involving the Decatur, the first time in over a year the Chinese navy conducted a provocative naval encounter with a U.S. warship.
Increased U.S.-China tensions come as Vice President Mike Pence outlined a new hardline Trump administration policy toward China.
"China wants nothing less than to push the United States of America from the Western Pacific and attempt to prevent us from coming to the aid of our allies," Pence said Oct. 4.
On the near collision of the warships, Pence said bluntly: "We will not be intimidated; we will not stand down."
Pence said the United States continues to support Taiwan. "America will always believe Taiwan’s embrace of democracy shows a better path for all the Chinese people," he said.
The Taiwan Strait warship passage also followed a meeting in Singapore between Defense Secretary Jim Mattis, who has sought to preserve worsening U.S.-China military ties, and Chinese Defense Minister Gen. Wei Fenghe.
Randy Schriver, assistant defense secretary for Asian and Pacific affairs, told reporters in Singapore that the Chinese requested the Singapore meeting on the sidelines of an Association of Southeast Asian Nations defense ministers' conference.
The Chinese defense chief "raised Taiwan and concerns about our policy," Schriver said.
"The secretary reassured Minister Wei that we haven’t changed our Taiwan policy, our one China policy," he added.
The Trump administration is currently locked in a trade war with China over Beijing's unfair trade practices, including large-scale theft of American technology and other intellectual property.
A visit by Mattis to China as part of the visit to Singapore and Vietnam was canceled after Beijing declined to make a high-ranking defense official available to meet Mattis.
China did not immediately comment on the Taiwan Strait warship transit but Beijing in the past has denounced such passages as military provocations.
Beijing, however, criticized the port visit to Taiwan's Kaohsiung port by a Navy research ship, USNS Thomas G. Thompson.
Taiwan said the Thompson was visiting Taiwan on a non-military scientific research project with a Taiwan university.
Mattis said on his way to Southeast Asia that the United States and China are "two Pacific powers, two economic powers."
"There’s going to be times we step on each other’s toes, so we’re going to have to find a way to productively manage our relationship," he said.
The defense secretary added that "we seek a relationship with China that's grounded in fairness, reciprocity, and respect for sovereignty, and that means respect for international rules and for all nations' sovereignty, whether they're large or small."
Mattis said the United States was "highly concerned" by China's militarization of disputed South China Sea islands.
During Mattis' visit to China in June, he met with Chinese President Xi Jinping. Xi was quoted in state media after the meeting that China would not give up an inch of territory in the sea.