President Joe Biden's Pentagon chief said the United States remained committed to supporting "Taiwan's ability to defend itself."

In a speech devoted largely to an array of challenges posed by an increasingly confident China, he underlined Washington's "real differences" with Beijing.

Austin was speaking at a national defense forum at the Reagan Presidential Library in Simi Valley, California.

In recent months, the Chinese military has mounted an increasingly aggressive series of sea and air military operations near Taiwan, which it claims as its own.

"It looks a lot like them exploring their true capabilities," Austin said. "It looks a lot like rehearsals."

Some analysts have suggested Beijing may be testing Biden during his first year in office.

China was the only power now capable of using its "economic, diplomatic, military and technological power to mount a sustained challenge to a stable and open international system," Austin said.

The world's two largest economic powers, he went on, have "real differences both over interests and values. But the way that you manage them counts."

He said Chinese leaders had been increasingly vocal about their "dissatisfaction with the prevailing order -- and about their aim of displacing America from its global leadership role."

But, Austin said: "We seek neither confrontation nor conflict.... We're not seeking a new Cold War or a world divided into rigid blocs."

In the face of the Chinese challenge, the retired four-star army general said, the US would be deepening its ties to friendly countries in the region, including through joint exercises.

"We remain steadfast to our One-China policy," Austin said, but also to "our commitments of the Taiwan Relations Act to support Taiwan's ability to defend itself while also maintaining our capacity to resist any resort to force that would jeopardize the security of the people of Taiwan."