The United States is tracking a suspected Chinese surveillance balloon that was spotted over American airspace for several days, but the Pentagon decided not to shoot it down due to concerns about injuring people on the ground, officials said Thursday. The discovery of the balloon further strains relations between the US and China at a time of heightened tensions.

A senior defense official told Pentagon reporters that the US had "very high confidence" that it was a Chinese high-altitude balloon flying over sensitive locations to gather information. One of the places where the balloon was spotted was Montana, which is home to one of the nation's three nuclear missile forces at Malmstrom Air Force Base. The official spoke on condition of anonymity to discuss sensitive information.

Brig. Gen. Patrick Ryder, the Pentagon press secretary, provided a brief statement on the matter, saying the government was continuing to track the balloon. He said it "currently travels at an altitude well above commercial air traffic and poses no military or physical threat to people on the ground".

He said similar balloon activity has been seen in the past few years. He added that the US has taken steps to ensure that it does not collect sensitive information.

A senior administration official, who was also not authorized to publicly discuss sensitive information, said President Joe Biden had been briefed and asked the military to present options. Defense Secretary Lloyd Austin and Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, advised against "kinetic actions" because of the risk to the safety of people on the ground. Biden accepted the recommendation.

A defense official said the US had "engaged" Chinese officials through several channels and communicated the seriousness of the matter.

The incident comes as Foreign Secretary Antony Blinken is set to make his first trip to Beijing, expected this weekend, to try to find common ground. Although the trip has not been officially announced, both Beijing and Washington have spoken of his imminent arrival.

It was not immediately clear whether the discovery of the balloon would affect Blinken's travel plans.

A senior defense official said the US had fighter jets, including F-22s, ready to shoot down the balloon if ordered by the White House. The Pentagon eventually recommended it, noting that even though the balloon was over a sparsely populated area of ​​Montana, its size would create a debris field large enough to endanger people.

It was not clear what the military was doing to prevent it from collecting sensitive information, or what would happen to the balloon if it was not shot down.