At a time of heightened tensions across the Taiwan Strait, Taiwan’s air force scrambled on Sunday to warn off eight Chinese aircraft, including fighter jets, that approached its air defense zone, according to the defense ministry.

For a year or more, Taiwan has complained about Chinese air force sorties near the self-ruled island, particularly in the southern area of its air defense zone near the Taiwan-controlled Pratas Islands.

The Chinese aircraft included six J-16 fighters, one anti-submarine aircraft, and one surveillance aircraft, according to a statement released late Sunday by the defense ministry.

Taiwan, which China claims as its own and has not ruled out taking by force, says Chinese military activities near the island jeopardize regional stability and repeatedly vows to defend its freedom and democracy.

According to a senior State Department official, US Secretary of State Antony Blinken reminded his Chinese counterpart on Sunday that the US opposes Chinese activities that have heightened tensions across the Taiwan Strait.

Blinken made “very clear” during an hour-long discussion with Chinese Foreign Minister Wang Yi on the sidelines of a Group of 20 summit in Rome, the official said, that Washington opposes any unilateral alterations to the status quo by Beijing.

According to China’s foreign ministry, Wang told Blinken that tensions over Taiwan were created by US assistance for pro-independence elements on the island.

A recent increase in Chinese military exercises in Taiwan’s air defense identification zone is part of what Taipei views as stepped-up military harassment by Beijing.

Taiwan President Tsai Ing-wen says the island is an independent country and has made modernizing the armed forces, which is well-armed but dwarfed by China’s, a top priority.

Earlier this month, Taiwan reported 148 Chinese air force planes in the southern and southwestern theatre of the zone over a four-day period, marking a dramatic escalation of tension between Taipei and Beijing.

Chinese aircraft have not been flying in Taiwan’s air space, but rather its air defense identification zone or ADIZ, a broader area Taiwan monitors and patrols that acts to give it more time to respond to any threats.