Taiwan reported renewed Chinese military activity around the island on Sunday, with nine aircraft crossing the sensitive median line of the Taiwan Strait and warships carrying out "combat readiness patrols."

Democratically-governed Taiwan, which China claims as its own territory, has complained for the past four years of regular Chinese military patrols and drills near the island, as Beijing seeks to pressure Taipei over its sovereignty claims.

With Chinese President Xi Jinping in San Francisco last week for the Asia Pacific Economic Cooperation (APEC) summit, where he met U.S. President Joe Biden, the scale of that military activity around Taiwan had scaled off.

But Taiwan's defense ministry reported that starting onSunday morning it had detected nine Chinese aircraft crossing the Taiwan Strait's median line, which had previously served as an unofficial barrier between the two and which Chinese planes now regularly fly over.

The aircraft involved included Su-30 and J-10 fighters, as well as early warning and electronic warfare aircraft, the ministry said.

The aircraft were accompanying Chinese warships carrying out "joint combat readiness patrols" it added.

Taiwan sent its own forces to monitor, the ministry said.

China's defense ministry did not answer calls seeking comment. China says its activities near Taiwan are aimed at "collusion" between Taiwan separatists and the United States and to protect China's territorial integrity.

Taiwan's government, which has repeatedly offered talks with China, rejects Beijing's sovereignty claims and says only the island's people can decide their future.

Taiwan was a major focus of the Biden-Xi talks in San Francisco.

Xi told Biden during their four-hour meeting on Wednesday that

Taiwan was the biggest, most dangerous issue in U.S.-China ties, according to a senior U.S. official.

Taiwan holds presidential and parliamentary elections on Jan. 13, with the island's fraught relations with China an important topic on the campaign trail.

Over the past year and a half China has staged two large-scale war games around Taiwan, though China's air force has not flown over the island or into its territorial air space.