By Raffi BergBBC News

China has staged one of its biggest incursions in the seas and skies around Taiwan, the island's government says.

It said that 71 Chinese air force planes, including fighter jets and drones, had entered Taiwan's so-called air defence identification zone.

The US said China's military activity was "destabilising" and undermined "regional peace and stability".

Taiwan is self-ruled - but China sees it as a breakaway province with which it will eventually reunite.

Tensions between the two sides have steadily increased in recent months.

In August, Beijing was enraged by a visit to the island by US Speaker of the House of Representatives Nancy Pelosi, the most senior US politician to visit Taiwan in 25 years.

China responded to that visit by holding what was then its biggest-ever military exercises in the seas around Taiwan, and also blocked some trade with the island.

Taiwan's foreign minister Joseph Wu condemned China's action then as highly provocative. China has never said it would not use force to bring Taiwan under its control.

On Monday, Taiwan's defence ministry said 43 Chinese aircraft had crossed over the so-called median line, an unofficial buffer separating the two sides inside the air defence zone.

China said it had conducted "strike drills" around Taiwan on Sunday in response to what it said was provocation from the island and the US.

A White House National Security Council official said the US was concerned by the latest development, adding it would "continue to assist Taiwan in maintaining a sufficient self-defence capability in line with our long-standing commitments and consistent with our one-China policy".

Washington has always walked a diplomatic tightrope over the issue of Taiwan.

On the one hand it adheres to the one-China policy, a cornerstone of its relationship with Beijing. Under this policy, the US acknowledges that there is only one Chinese government, and has formal ties with Beijing rather than Taiwan.

But it also maintains close relations with Taiwan and sells arms to it under the Taiwan Relations Act, which states that the US must provide the island with the means to defend itself.

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