Chinese technology company Huawei can secretly access phone networks, American officials say.
A Wall Street Journal report claims Huawei maintains back door access to telecom networks around the world through channels designed for law enforcement.
Huawei denies the allegations.
American president Donald Trump signed an executive order in May last year against Huawei prohibiting American companies from licensing technology to the Chinese company. However the reasons for that have been shrouded in secrecy.
But now United States security officials are saying Huawei has maintained back door access into some of the networks it builds, starting as early as 2009 with 4G equipment.