BEIJING (AP) — China on Monday accused the United States of indiscriminate use of force when the American military shot down a suspected Chinese spy balloon Saturday.

The U.S. shot down a balloon off the Carolina coast after it traversed sensitive military sites across North America. China insisted the flyover was an accident involving a civilian aircraft.

Vice Foreign Minister Xie Feng said he lodged a formal complaint with the U.S. Embassy on Sunday over the “U.S. attack on a Chinese civilian unmanned airship by military force.”

The presence of the balloon in the skies above the U.S. dealt a severe blow to already strained U.S.-Chinese relations that have been in a downward spiral for years. It prompted Secretary of State Antony Blinken to abruptly cancel a high-stakes Beijing trip aimed at easing tensions.

Xie repeated China’s insistence that the balloon was a Chinese civil unmanned airship that blew into U.S. mistake, calling it “an accidental incident caused by force majeure.”

U.S. President Joe Biden issued the shootdown order after he was advised that the best time for the operation would be when it was over water, U.S. officials said. Military officials determined that bringing down the balloon over land from an altitude of 60,000 feet (18,000 meters) would pose an undue risk to people on the ground.

“What the U.S. has done has seriously impacted and damaged both sides’ efforts and progress in stabilizing Sino-U.S. relations since the Bali meeting,” Xie said, referring to the recent meeting between Biden and his Chinese counterpart Xi Jinping in Indonesia that many hoped would create positive momentum for improving ties that have spiraled to their lowest level in years.