WASHINGTON: The Chinese balloon downed by the US last weekend was part of a sprawling fleet likely operated by Beijing's military to conduct surveillance operations worldwide, the Biden administration said Thursday.

The fleet has been used to surveil more than 40 countries across five continents and the US is currently in the process of contacting affected nations to discuss the matter, a State Department official said on condition of anonymity due to the sensitive nature of disclosures.

The high-altitude balloons are set up to collect sensitive information, including communications, and the equipment they carry is "inconsistent with the equipment onboard weather balloons," said the official, according to Anadolu Agency.

The US assessment is based in part on high-resolution imagery of the balloon collected by U-2 reconnaissance planes as the balloon transversed the US beginning last week at an altitude of more than 60,000 feet (18,288 metres), much higher than most planes are capable of flying. That necessitated the use of the Cold War-era U-2s, which can reach altitudes up to 70,000 feet.

The US releasing its assessment is meant to publicly refute China's narrative that the aircraft was a weather balloon that had been blown off course. Washington's downing of the balloon Saturday has further exacerbated US-Sino tensions as Beijing maintained its narrative and claimed the US was overreacting.

"From the PRC's messaging and public comments, it's clear that they have been scrambling to explain why they violated US sovereignty and still have no plausible explanation - and have found themselves on their heels," said the State Department official.

The US is "confident" that the balloon manufacturer "has a direct relationship with China's military and is an approved vendor of the" Chinese military, formally known as the People's Liberation Army (PLA), said the official. The assessment is based on information published in an official procurement portal for the PLA.

"The company also advertises balloon products on its website and hosts videos from past flights, which appear to have overflown at least US airspace and airspace of other countries," the official said in an emailed statement.

"These advertised balloon videos seemingly have similar flight patterns as the balloons we have been discussing this week," it said.

The company was not explicitly identified but the official said the Biden administration is weighing potential sanctions on "entities linked to the PLA that supported the balloon's incursion into US airspace".

-- BERNAMA