The Pentagon said Thursday it was tracking a Chinese spy balloon flying high over the United States, reviving tensions between the two countries just days ahead of a rare visit to Beijing by the top US diplomat.

At President Joe Biden's request, Defense Secretary Lloyd Austin and top military officials considered shooting the balloon down but decided doing so would endanger too many people on the ground, a senior defense official told reporters Thursday.

"Clearly, the intent of this balloon is for surveillance," said the official, who spoke on condition of anonymity.

"Clearly, the intent of this balloon is for surveillance," said the official, who spoke on condition of anonymity.

The official added that the balloon had flown over the northwest United States, where there are sensitive airbases and nuclear missiles in underground silos,

but that the Pentagon did not believe it constituted a particularly dangerous intelligence threat.

but that the Pentagon did not believe it constituted a particularly dangerous intelligence threat.

"We assess that this balloon has limited additive value from an intelligence collection perspective," the official said.

The discovery of the aircraft comes just days before an expected visit to China by US Secretary of State Antony Blinken, with managing heightened tensions between the two powers at the top of the agenda.

Blinken's visit to Beijing, which follows a meeting last November between Biden and Chinese President Xi Jinping on the sidelines of the G20 summit, will be the first trip to the Asian country by the United States' top diplomat since 2018.