US Ambassador to Germany Richard Grenell has sent a letter to the German government threatening to curtail access to American intelligence if Berlin decides to issue contracts to Chinese tech giant Huawei to build their 5G communications networks, the media reported.
"The Federal Minister for Economic Affairs and Energy has indeed received a letter; there is no comment on its content from their side. There will be a quick reply," CNN quoted Matthias Wehler, spokesperson at the German embassy in Washington D.C., as saying on Monday.
Germany announced on March 7 that it wouldn't ban any company from bidding on 5G contracts.
The State Department has not commented on Grenell's letter, but Garrett Marquis, a National Security Council spokesperson, outlined how Huawei's 5G networks could pose a constantly evolving and shifting threat.
"Because 5G networks are largely software-defined, updates pushed to the network by the manufacturer can radically change how they operate," Marquis told CNN.
"The 5G networks our allies buy won't be the networks that they eventually operate, as the software could be changed on a moment-to-moment basis by the manufacturer."
The letter follows similar warnings by President Donald Trump's administration urging allies to ban or restrict Huawei products from their 5G networks due to its ability to compromise national security by selling equipment with "backdoors" that could allow for unauthorised surveillance.
China and Huawei have vigorously pushed back on the US charges and the telecom giant last week filed a suit against Washington over the 2019 National Defence Authorization Act, which bans American federal agencies from buying Huawei products.
The lawsuit is Huawei's most aggressive move yet to fight back against US claims.
Germany's March 7 announcement follows a similar decision by the UK. Both countries argue they can mitigate any risks and their decisions could make it harder for Washington to convince smaller countries to follow suit.
Security concerns have led Australia to completely ban the company's technology and New Zealand has moved to partially restrict it.
The 5G network is the next generation of wireless networks that promises to be 100 times faster and more reliable than current technology.
It is a market that will be worth billions, as 5G will require compatible new phones and communications equipment.