One of the places balloon was spotted was Montana, home to one of America's three nuclear missile silo fields at Malmstrom Air Force Base, defence officials say.
United States is tracking a Chinese spy balloon flying high over the western region, the Pentagon has said.
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 defence official told reporters on Thursday.
Another defence official told Pentagon reporters that the US has "very high confidence" it is a Chinese high-altitude balloon and it was flying over sensitive sites to collect information.
Brigadier General Patrick Ryder, Pentagon press secretary, provided a brief statement on the issue, saying the government continues to track the balloon. He said it is "currently travelling at an altitude well above commercial air traffic and does not present a military or physical threat to people on the ground."
One of the places the balloon was spotted was Montana, which is home to one of the nation’s three nuclear missile silo fields at Malmstrom Air Force Base.
The official said that Washington had been tracking the balloon since it entered US airspace a couple of days ago, including by observing it with manned US military aircraft.
The official spoke on condition of anonymity to discuss sensitive information.
The Pentagon announcement comes days before Secretary of State Antony Blinken is expected to travel to China.
It's not clear if this will affect his travel plans, which the State Department has not formally announced.