U.S. officials say Huawei can access mobile phone networks around the world through back doors designed for use by law enforcement.

"We have evidence that Huawei has the capability secretly to access sensitive and personal information in systems it maintains and sells around the world," Robert O'Brien, national security adviser, reportedly said.

U.S. intelligence shows that Huawei has had this capability for more than a decade. The U.S. kept this information classified until late last year when it provided details with allies like Germany and the U.K. to prevent from using Huawei equipment.

U.S. officials claim that Huawei has built equipment that preserves its ability to access networks through interfaces without the carriers' knowledge. Officials have not provided the details of where they believe Huawei can do so.

Officials declined to say whether the U.S. has observed Huawei using this access. There are no details to be provided about the alleged backdoor access, except they have been aware since 2009 in early 4G cellular equipment.

The U.S. government's allegation against Huawei highlights a security argument that the U.S. has long been wrangling with tech companies.

The U.S. has for years pressured big tech companies to build methods for allowing law enforcement to circumvent security measures like encryption.

"The U.S. government's concern about possible backdoors in Huawei-built networks only underscores why it is untenable for the government to demand that US-based tech companies create backdoors for domestic law enforcement agencies. Once built, these mechanisms can be co-opted by governments around the world," Andrew Crocker, Senior Staff Attorney at the Electronic Frontier Foundation said.

Huawei has consistently denied the reports and said it has never spied on behalf of any country and would refuse any request to spy for Bejing.

"U.S. allegations of Huawei using lawful interception are nothing but a smokescreen," Huawei said in an emailed statement. "Huawei has never and will never covertly access telecom networks, nor do we have the capability to do so."