U.S. Secretary of State Antony Blinken said Friday he has put off a visit this weekend to Beijing after a Chinese spy balloon was detected traveling over the continental United States, calling its flight an "irresponsible act" that is "detrimental" to efforts to improve relations.

Blinken said he informed Wang Yi, China's top foreign policy official, of the postponement in a phone call, telling reporters that the presence of the balloon in U.S. skies is a "clear violation" of the country's sovereignty and international law and that it undermined the purpose of the long-planned trip.

U.S. Secretary of State Antony Blinken speaks at a press conference on Feb. 3, 2023, in Washington. (Kyodo)

The top U.S. diplomat, however, said lines of communication with China remain open given the significance of the relationship, both to the two nations and to the rest of the world, and that he would reschedule the trip "when conditions allow."

"But the most important thing right now in the moment is to see that this asset gets out of our airspace and we will take it from there," he said in a press conference after holding talks with his South Korean counterpart Park Jin in Washington.

The postponement came a day after the discovery of the balloon was announced by the U.S. Defense Department, with the incident again reflecting the complex and often thorny relationship between the two countries.

The Pentagon revealed Friday that the balloon, which had entered U.S. continental airspace a "couple of days ago" and was flying above the western state of Montana, is now floating eastward at an altitude of about 18 kilometers above the central part of the country.

The United States has chosen not to shoot the balloon down because the flying object is large enough to warrant concern that people on the ground could be injured by debris.

Pat Ryder, the Defense Department's press secretary, said it is still reviewing all options, while the North American Aerospace Defense Command continues to monitor the object.

China had released a statement of regret, saying the balloon was used for meteorological research and deviated far from its intended course due to westerlies and limited control capability.

But Ryder flatly rejected the Chinese claim that it is not a spy balloon. He said that based on close assessment by the United States, it is clear the balloon has the ability to maneuver and change course and is being used for espionage, while noting it was posing no threat, either physically or militarily.

He declined to offer information on how China controls its flight path or how it is powered.

Following the U.S. accusations, China's Foreign Ministry said that Wang, during the phone conversation with Blinken, stressed that the country has always strictly followed international law and that it can "not accept any groundless speculation and hype."

Blinken was set to make his first trip to Beijing for follow-up talks after President Joe Biden and Chinese President Xi Jinping held their first face-to-face meeting as leaders of their respective countries in November.

During the meeting, held on the sidelines of a Group of 20 summit in Indonesia, the two presidents agreed to facilitate communication, despite very different positions on Taiwan, Russia's invasion of Ukraine, and economic and human rights issues.

The trip, which was due to begin Friday night, would have been the first by a sitting U.S. secretary of state in more than four years.

White House spokeswoman Karine Jean-Pierre said Friday that Biden agreed that Blinken should refrain from traveling to China just now.

She told reporters that Biden was first briefed on the balloon on Tuesday and asked the military to present options.

Defense Secretary Lloyd Austin and Joint Chiefs of Staff Chairman Mark Milley strongly recommended not to take "kinetic action," citing the risk to safety of civilians on the ground, she added.

The discovery of the balloon has led to renewed calls among U.S. lawmakers for more pressure on China.

Mike Gallagher, a Republican chair of the recently established Select Committee on China of the House of Representatives, and Raja Krishnamoorthi, a Democrat who serves as the ranking member of the panel, said this incident shows the Chinese Communist Party's threat "is not confined to distant shores."

"It is here at home and we must act to counter this threat," they said in a joint statement.

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