"We made clear to the ambassador that Beijing's actions are of concern to Taiwan, to us, and to our partners around the world," Kirby said, highlighting concerns from the G7 group of wealthy democracies and the Asian regional grouping ASEAN.

"Finally, we made clear once again as we have done privately at the highest levels and publicly: nothing has changed about our one China policy," Kirby said.

He was referring to the US position of only acknowledging the Chinese position that Taiwan is part of China.

It leaves it to the two sides to work out a solution, while opposing any use of force to change the status quo.

Beijing insists that Taiwan is a part of China awaiting reunification, by force if necessary. Taiwan's current ruling party has vowed to defend the island's sovereignty.

"We also made clear that the United States is prepared for what Beijing chooses to do. We will not seek and do not want a crisis," he said.

"At the same time, we will not be deterred from operating in the seas and skies of the Western Pacific, consistent with international law, as we have for decades -- supporting Taiwan and defending a free and open" Pacific region.