The US threatened to cut back on intelligence sharing with Germany if it allows operators to use Huawei equipment in their 5G networks, The Wall Street Journal (WSJ) reported.
In a letter to German officials reviewed by the newspaper, the US ambassador to the country Richard Grenell warned use of kit from companies including Huawei and ZTE could compromise the security of information exchanges between defence partners.
While intelligence sharing would not cease entirely if Germany allows Chinese equipment, Grenell said it would not continue at the same level. The ambassador went on to suggest Ericsson, Nokia and Samsung as alternative 5G equipment suppliers.
The official notice followed an informal warning issued by US Secretary of State Mike Pompeo in February, who said the presence of Huawei kit in overseas networks would make it more difficult to partner with those countries due to security concerns.
German regulators last week unveiled a plan to implement more stringent security requirements for operators. However, the draft regulations did not explicitly prohibit any equipment provider.
Huawei and ZTE repeatedly denied they pose a threat, with Huawei rotating chairman Guo Ping arguing at MWC19 Barcelona the US has no evidence to back up its claims.