The former head of the US Central Intelligence Agency and National Security Agency said Chinese telecommunications giant Huawei has spied for Beijing.

Michael Hayden accused Huawei of supplying the Chinese government with “intimate and extensive knowledge of the foreign telecommunications systems it is involved in,” The Australian Financial Review reports.

He said it was his “professional judgement” that Huawei is a significant threat to Australia and the US, and that intelligence agencies have evidence of its clandestine activities.

The remarks could damage Huawei, the world’s largest telecoms infrastructure supplier, which has constantly run into obstacles in expanding its businesses in the US, the UK, Australia, and elsewhere.

Huawei embarked on an extensive lobbying campaign in Australia to bid for work in building its National Broadband Network. The federal government banned Huawei from the project in 2011.

John Suffolk, Huawei’s global security officer, rebuked Hayden’s comments as “tired, unsubstantiated, and defamatory,” and said critics should present evidence publicly.

Security analysts have long feared that the company’s links to the Chinese government would make nations which embedded Huawei’s equipment in its telecoms infrastructure vulnerable to cyber espionage by Beijing, reports the Financial Times.