The US Navy and Coast Guard were using underwater drones overnight on Tuesday to locate and map the debris field of a downed Chinese balloon.
The suspected surveillance balloon was shot down off the South Carolina coast on Saturday after a days-long journey across the US mainland.
Navy divers began pulling pieces of the suspected spy balloon from the ocean floor after all the balloon's pieces floating on the surface were collected earlier on Tuesday.
The debris will eventually go either to the FBI lab at Quantico, Virginia, or other sites where experts can analyze it, officials, who spoke on condition of anonymity, told the Associated Press.
US convinced of a Chinese surveillance program
The Washington Post reported on Tuesday that US intelligence has linked the balloon to a vast surveillance program run by China across the globe.
Unnamed officials told the newspaper the surveillance airships, operated by the Chinese military, have been spotted over five continents.
The US believes such balloons were used to collect intelligence on strategically relevant territories.
On Monday, Deputy Secretary of State Wendy Sherman briefed representatives of around 40 embassies about the surveillance program.
"We want to make sure that we are sharing as much as we can with countries around the world who may also be susceptible to these types of operations," the senior administration official said.
Meanwhile, China denied using such balloons for surveillance.
On Tuesday, China's Foreign Ministry spokesperson Mao Ning blamed the US of overreacting.
She said that the US should handle such incidents "in a calm and professional manner" without using force.
Downturn in Sino-US relations
President Joe Biden said in his State of the Union address that the US would act to protect itself should China threaten its sovereignty, but he kept the door open to cooperation.
He said he was committed to working with China where it could advance US interests and benefit the world.
"But make no mistake about it: as we made clear last week, if China threatens our sovereignty, we will act to protect our country. And we did," Biden added.
In reaction to the speech, China said it would "firmly defend" its interests and urged the United States to work on repairing relations.
"We will firmly defend China's sovereignty, security, and development interests," Mao Ning said.
