Taiwan reported Chinese warplanes and warships around the island on Saturday, including aircraft crossing the sensitive median line of the Taiwan Strait, as Beijing continues military activities with three weeks to go before Taiwan votes.

Democratically governed Taiwan, which China claims as its own territory, has complained for four years of regular Chinese military patrols and drills near the island.

Campaigning is under way for Taiwan’s Jan. 13 presidential and parliamentary polls. Relations with China are a major point of contention.

Taiwan’s defense ministry said that since 1:30 p.m. (0530 GMT) on Saturday it had detected J-10, J-11 and J-16 fighters as well as early warning aircraft operating in the airspace to north, middle and southwest of Taiwan.

Ten aircraft crossed the Taiwan Strait median line, or areas close by, working with Chinese warships to carry out “joint combat readiness patrols”, the ministry said.

The median line once served as an unofficial barrier between the two sides, but Chinese planes now regularly fly over it.

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

China has not commented on its recent spate of military activities near Taiwan. It has previously described them as being aimed at preventing “collusion” between Taiwan separatists and the United States, and protecting 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.

The ruling Democratic Progressive Party’s Lai Ching-te, whom Beijing has denounced as a separatist, is the frontrunner to be Taiwan’s next president, according to opinion polls.

Taiwan’s main opposition party, the Kuomintang, traditionally supports close ties with Beijing, and has pledged to reopen dialogue with China if it wins the election. But it too also says Taiwan’s people are the only ones who can decide their future.