Michael Hayden, the former head of the CIA and National Security Agency, said yesterday it "goes without saying" that Chinese telecoms giant Huawei spies for Beijing.
Huawei, however, strongly denied Hayden's allegations.
Speaking to the Australian Financial Review, Hayden claimed China was engaged in unrestricted espionage against the West and said it was his belief that Huawei would have shared information with state agencies.
Asked whether Huawei represented an unambiguous national security threat to the US and Australia, Hayden replied: "Yes, I believe it does."
Britain, the US and Australia have all raised concerns that Huawei's alleged ties to the Chinese state could see their telecoms infrastructure used for spying and cyberattacks.
Huawei's global cybersecurity officer John Suffolk, who has previously described the company as the "piggy in the middle" of the broader dispute over hacking between China and the United States, reportedly dismissed Hayden's comments. as tired, unsubstantiated and defamatory.
"It's time to put up or shut up," said Suffolk. Huawei's global cyber security officer, told the newspaper.
He described the comments made by Hayden as "tired, unsubstantiated defamatory remarks" and challenged him and other critics to present any evidence publicly.
"Huawei meets the communication needs of more than a third of the planet and our customers have the right to know what these unsubstantiated concerns are," Suffolk said.
The US Congress last year called for its exclusion from US government contracts. It was also barred from bidding for contracts to build Australia's national broadband network.
Hayden, a retired general, said he believed Western intelligence networks had hard evidence that Huawei had spied on behalf of the Chinese state.
"I have no reason to question the belief that's the case," said Hayden, who retired from the CIA in 2009 and who prior to that served as head of the National Security Agency (NSA).
"That's my professional judgment. But as the former director of the NSA, I cannot comment on specific instances of espionage or any operational matters.
"At a minimum, Huawei would have shared with the Chinese state intimate and extensive knowledge of the foreign telecommunications systems it is involved with. I think that goes without saying."
Hayden said Huawei had approached him several years ago to be on the firm's American board, but failed to convince him it should be involved in critical communications infrastructure.
"This is not blind prejudice on my part. This was my considered view based on a four-decade career as an intelligence officer," he said.
"My conclusion was that it is simply not acceptable for Huawei to be creating the backbone of the domestic telecommunications network in the US."
Hayden is a director of Motorola Solutions, which provides radios, smart tags, barcode scanners and safety products. Huawei and Motorola Solutions had previously been engaged in intellectual property disputes for a number of years.
Hayden's remarks came a day after Britain announced it would review security at a cyber centre in England run by Huawei to ensure the British telecommunications network is protected.
The British government asked its National Security Adviser Kim Darroch to review the workings of a Huawei facility known as "the Cell".
Huawei, the world's second-largest maker of equipment for phone networks after Ericsson, was founded by Ren Zhengfei in 1987 after retiring from the Chinese military in 1983.
Additional reporting by Associated Press