SEOUL - Two United States Navy warships have entered the Taiwan Strait in what is the first US naval transit in the waterway since US-China tensions spiked this month over a visit to the island by House Speaker Nancy Pelosi.

The guided-missile cruisers USS Antietam and USS Chancellorsville were on Sunday making the voyage “through waters where high seas freedoms of navigation and overflight apply in accordance with international law,” the US 7th Fleet in Japan said in a statement.

It said the transit was “ongoing” and that there had been “no interference from foreign military forces so far.”

“These ships (are transiting) through a corridor in the strait that is beyond the territorial sea of any coastal state. The ships’ transit through the Taiwan Strait demonstrates the United States’ commitment to a free and open Indo-Pacific. The United States military flies, sails, and operates anywhere international law allows,” it said.

John Kirby, a spokesperson for the National Security Council, told CNN’s Jim Sciutto on Sunday that the two US Navy warships transiting the Taiwan Strait sent a “very clear” and “very consistent” message that “the United States military will sail, fly and operate wherever international law permits us to do so.” “This was planned long ago,” Kirby added.

The Chinese military’s Eastern Theater Command said it was monitoring the two ships, maintaining a high alert and was “ready to thwart any provocation.” The strait is a 110-mile (180-kilometer) stretch of water that separates the democratic self-ruled island of Taiwan from mainland China.

Beijing claims sovereignty over Taiwan despite China’s ruling Communist Party never having controlled the island -- and considers the strait part of its “internal waters.”

The US Navy, however, says most of the strait is in international waters. The Navy cites an international law that defines territorial waters as extending 12 nautical miles (22.2 kilometers) from a country’s coastline and regularly sends its warships through the strait in what it calls freedom of navigation operations, including recent voyages by the guided missile destroyers USS Benfold and USS Port Royal.

Those transits drew angry responses from Beijing. “The frequent provocations and showing-off by the US fully demonstrate that the US is the destroyer of peace and stability in the Taiwan Strait and the creator of security risks in the Taiwan Strait,” Col. Shi Yi, spokesman for the People’s Liberation Army’s Eastern Theater Command, said after the Benfold’s transit on July 19. Beijing has ramped up military maneuvers in the strait -- and the skies above it -- following the visit by Pelosi to the island earlier this month.

Within minutes of Pelosi landing in Taiwan on August 2, the PLA announced four days of military exercises in six zones encircling the island. The maneuvers included launching ballistic missiles into waters around Taiwan, numerous Chinese warships steaming in the Taiwan Strait and dozens of PLA warplanes breaching the median line -- the midway point between mainland China and Taiwan that Beijing says it does not recognize but had largely respected.

| The guided-missile cruisers USS Antietam and USS Chancellorsville making voyage “through waters where high seas freedoms of navigation and overflight apply in accordance with international law