Two US warships made a “routine passage” through the Taiwan Strait on Monday, in a move that is sure to ruffle feathers in Beijing as its relations with Washington continue to deteriorate.

A guided-missile destroyer and guided-missile cruiser both made the politically sensitive trip, the first such voyage by US vessels since July.

The move “demonstrates the US commitment to a free and open Indo-Pacific,” spokesman for the US Pacific Fleet Commander Nate Christensen was quoted by The Wall Street Journal as saying. “The US Navy will continue to fly, sail and operate anywhere international law allows,” he stressed.

Since the US normalized relations with China, its relationship with Taiwan has been an area of recurring friction with Beijing, though Washington has tended to tread carefully.

Under the Trump administration, a greater frequency of arms sales to Taipei coupled with the passage of the Taiwan Travel Act, which encourages US government officials to visit Taiwanese counterparts, has increased tensions.

Following the sailing of US ships through the Taiwan Strait in July, Beijing’s top official for Taiwan affairs decried what he described as playing the “Taiwan card.”

Last month, after the US authorization of a US$330 million arms sale to Taiwan, China’s foreign ministry spokesman said the move “undermines China’s sovereignty and security interests,” adding that Beijing expressed its “strong dissatisfaction” and “resolute opposition.”