Detailed images taken by high-altitude U2s showed the balloon's payload equipment "was clearly for intelligence surveillance and inconsistent with the equipment onboard weather balloons," the senior State Department official said.

"It had multiple antennas to include an array likely capable of collecting and geo-locating communications," the official said in a statement.

"It was equipped with solar panels large enough to produce the requisite power to operate multiple active intelligence collection sensors," the official said, on grounds of anonymity.

A US fighter jet shot the balloon down over the Atlantic on Saturday after it had crossed much of the country, overflying areas where the US keeps nuclear missiles in underground silos and bases with strategic bombers.

The incident led US Secretary of State Antony Blinken to cancel an imminent trip to Beijing that had been long in planning and aimed at improving communications between the two rival superpowers.

- FBI examines recovered balloon material -

An official of the Federal Bureau of Investigation, which is tasked with examining the balloon, said Thursday that so far only a "very small" part of the balloon's payload of spying and power electronics has been recovered.

"The evidence that has been recovered and brought to the FBI is extremely limited," the official said, adding that it was being examined at the FBI's laboratories in Quantico, Virginia.

What was recovered so far was floating on the surface of the water, the official said, on grounds of anonymity.

The larger part of the payload, including sprawling solar panels, sunk in around 47 feet (14 meters) of water after the balloon was shot down.

The FBI did not say whether the main payload pieces had been located, but warned that looming bad weather could hinder the recovery.

The State Department official indicated that the US believes the balloon was under the control of the Chinese People's Liberation Army, and is part of a fleet of balloons that China has sent over more than 40 countries on five continents to collect intelligence information.

"We are confident that the balloon manufacturer has a direct relationship with China's military, " the official said.

The official said the United States was weighing taking action against Chinese entities linked to the balloon's operation, which suggests it might slap them with sanctions.

- Pentagon defends shootdown decision -

Earlier Thursday Beijing confirmed that it refused an overture on Saturday by US Defense Secretary Lloyd Austin for phone discussions with Chinese counterparts over the balloon issue.

"This irresponsible and seriously mistaken approach by the US did not create a proper atmosphere for dialogue and exchanges between the two militaries," China's defense ministry said in a statement.

In a Congressional hearing Thursday, US Assistant Secretary of Defense Melissa Dalton defended the Pentagon's decision not to shoot the balloon down when it first entered US airspace over the waters of Alaska on January 28.

Dalton said the cold and icy seas by Alaska, which plunge to around 18,000 feet in depth (5,486 meters), would have made recovery much more difficult and "extremely dangerous."

As it flew over Alaska and northwest Canada, she said, "We continued to track and assess the balloon, learning more about (China's) capabilities and tradecraft."