The United States on Saturday warned China that a recent incident involving an alleged spy balloon was unacceptable and should not be repeated, reported the Associated Press.

The United States said it gave the warning during a meeting between Secretary of State Antony Blinken and China’s Foreign Minister Wang Yi in Munich.

“I made very clear to him [Wang Yi] that China sending its surveillance balloon over the United States in violation of our sovereignty, was in violation of international law, was unacceptable and must never happen again,” Blinken said told CBS in an interview.

On February 4, the United States military shot down the suspected Chinese surveillance balloon off the coast of South Carolina, adding to already strained relations between Washington and Beijing.

The balloon had first entered the United States airspace in Alaska on January 28, before moving into Canadian airspace three days later, according to the BBC. It had then re-entered American airspace on January 31 and was seen in the state of Montana, where a number of sensitive nuclear missile sites are located.

Spy balloons, which were used extensively during the Cold War, have sophisticated cameras and imaging technology to collect information. They operate quite high in the sky, more or less where commercial aeroplanes are flown.

China has maintained that the ballon was merely a weather research “airship” that had deviated from its course.

Saturday’s meeting was the first between the officials of the two countries since the incident. Blinken had previously cancelled his visit to China slated for February 4.

During the meeting on Saturday, Blinken told Wang that the February 4 incident has exposed China’s “high-altitude surveillance balloon program” before the world, a release from his office said.

Washington believes that through its program, China violated the air space of over 40 countries across 5 continents.

Meanwhile, Wang told Blinken that their countries’ relations had been damaged by Washington’s reaction to the balloon incident, according to The Associated Press.

“The actions don’t show that the US is big and strong, but describe the exact opposite,” Wang said. “What we hope for from the US is a pragmatic and positive approach to China that allows us to work together.”