TAIPEI (Reuters) -China sent more fighter jets into Taiwan’s air defence zone on Wednesday in a stepped-up show of force around the island Beijing claims as its own, and Taiwan’s foreign minister said it would fight to the end if China attacks.

The democratic self-governed island has complained of repeated military activities by Beijing in recent months, with China’s air force making almost daily forays in Taiwan’s air defence identification zone. On Monday, China said an aircraft carrier group was exercising close to the island.

Taiwan’s Defence Ministry said 15 Chinese aircraft, including 12 fighters, entered its air defence identification zone, with an anti-submarine aircraft flying to the south through the Bashi Channel between Taiwan and the Philippines.

Taiwan’s air force sent up aircraft to intercept and warn the Chinese away, the ministry added.

Adding to the stepped-up military activity, the U.S. Navy said its John S. McCain guided missile destroyer conducted a “routine” transit of the Taiwan Strait on Wednesday.

China’s Eastern Theatre Command said it tracked the ship and denounced the United States for “endangering the peace and stability of the Taiwan Strait”.

Speaking earlier in the day, Taiwan Foreign Minister Joseph Wu said the United States was concerned about the risk of conflict.

“From my limited understanding of American decision makers watching developments in this region, they clearly see the danger of the possibility of China launching an attack against Taiwan,” he told reporters at his ministry.

“We are willing to defend ourselves without any questions and we will fight the war if we need to fight the war. And if we need to defend ourselves to the very last day we will defend ourselves to the very last day.”

In Washington, U.S. State Department spokesman Ned Price was asked about the Chinese activity and Wu’s comments and said the United States noted with “great concern” a pattern of ongoing Chinese intimidation efforts in the region, including towards Taiwan.