A US and a Canadian warship traveled through the Taiwan Strait on Saturday, according to the US Navy, in a rare combined operation in the sensitive waterway at a time when Beijing and Washington are at odds over Chinese-claimed Taiwan.

The USS Chung-Hoon and Canada’s HMCS Montreal made a “routine” transit of the strait, according to the US Navy’s 7th Fleet, “through waters where high-seas freedoms of navigation and overflight apply in accordance with international law.”

“Chung-Hoon and Montreal’s bilateral transit through the Taiwan Strait demonstrates the commitment of the United States and our allies and partners to a free and open Indo-Pacific,” it said in a statement.

While U.S. warships transit the strait around once a month, it is unusual for them to do so with those of other U.S. allies.

The mission took place as the U.S. and Chinese defense chiefs were attending a major regional security summit in Singapore.

At that event, U.S. Secretary of Defense Lloyd Austin rebuked China for refusing to hold military talks, leaving the superpowers deadlocked over Taiwan and territorial disputes in the South China Sea.

There was no immediate response to the sailing from China’s military, which routinely denounces them as a U.S. effort to stir up tensions.

The last such publicly revealed U.S.-Canadian mission in the narrow strait took place in September.

China has been ramping up military and political pressure in an attempt to force Taiwan to accept Beijing’s sovereignty claims, which the government in Taipei strongly rejects.