The Pentagon on Wednesday said the Chinese balloon shot down off the South Carolina coast Saturday was part of a program involving a number of such airships that China has been operating for “several years.”

At Thursday’s daily briefing, Chinese Foreign Ministry spokesperson Mao Ning repeated China’s insistence that the large unmanned balloon was a civilian meteorological airship that had accidentally blown off course and that the U.S. had “overreacted” by shooting it down.

“It is irresponsible,” Mao said at a daily briefing. The latest accusations “may be part of the U.S. side’s information warfare against China.”

China’s defense minister refused to take a phone call from Defense Secretary Lloyd Austin to discuss the balloon issue on Saturday, the Pentagon said, and China has not answered questions as to what government department or company the balloon belonged to, or how it planned to follow up on a pledge to take further action over the matter.

U.S. officials have dismissed China’s claims and agents from the FBI and the Naval Criminal Investigative Service are cataloguing debris recovered from the ocean and transporting it for further processing.

When similar balloons passed over U.S. territory on four occasions during the Trump and Biden administrations, the U.S. did not immediately identify them as Chinese surveillance balloons, said Brig. Gen. Pat Ryder, the Pentagon press secretary.

But he said “subsequent intelligence analysis” allowed the U.S. to confirm they were part of a Chinese spying effort and learn “a lot more” about the program.

“I can assure you this was not for civilian purposes … We are 100% clear about that,” Ryder said.

Top administration officials were briefing members of Congress on the Chinese balloon surveillance program in classified sessions on Wednesday and Thursday.

Secretary of State Antony Blinken canceled a visit to Beijing planned for this week in the wake of the incident, dealing a setback to efforts at arresting a further deterioration of bilateral relations that have spiraled to their lowest level in decades.

He said the U.S. has briefed dozens of countries on the program, which officials said has been active over five continents.

“The United States was not the only target,” he said at a news conference with visiting NATO chief Jens Stoltenberg.

Blinken said he and Stoltenberg had spoken about the “systemic and tactical challenges” that China poses to the alliance and the importance of combatting them.

With China’s tone sharpening over the balloon incident, it wasn’t clear when Blinken’s visit might be rescheduled.

Despite that, China’s Commerce Ministry said Thursday it welcomed a proposed visit by U.S. Treasury Secretary Janet Yellen, saying, “It’s very important for both sides to maintain normal communication.”