The U.S. Embassy in Berlin said on Monday that use of untrusted vendors by allies in their 5G mobile networks could jeopardise future sharing of intelligence by the U.S. government.
An embassy spokesman declined to comment specifically on a Wall Street Journal report about the U.S. government's first explicit warning to Germany of consequences if China's Huawei Technologies Co. gets a role in Germany's next-generation mobile infrastructure.
But he said the use of untrusted vendors in allies' networks could raise questions about the integrity and confidentiality of sensitive communications within a country, and between that country and its allies.
"This could in the future jeopardise nimble cooperation and some sharing of information," the spokesman said. "We are engaging intensively with our allies on how to secure our telecommunications networks to ensure continued interoperability."
U.S. Ambassador Richard Grenell issued the warning in a letter to German Economy Minister Peter Altmaier dated Friday, the Journal reported.
A spokesman for Altmaier said a letter had been received from the embassy, and the ministry would respond in a timely manner. "The letter is being evaluated," the spokesman said, although he declined to provide any details about its contents.
Altmaier told a television talk show on Thursday that Germany did not want to ban Huawei but would change its laws to ensure all components used in the 5G networks are secure.
The legal changes are still being finalised within Germany's ruling coalition, the ministry spokesman said.
In his letter, Grenell said that Chinese companies, under Chinese law, can be required to support China's security agencies and that inspections of Huawei software could not ensure there were no vulnerabilities, the newspaper said.
The battle with Huawei is one of many conflicts in Washington's disputes with China, but it is also exacerbating tensions in U.S.-German ties that are strained over the Nord Stream 2 gas pipeline, the 2015 Iran nuclear deal and trade.
The United States and China spent most of 2018 slapping import tariffs on billions of dollars worth of each other's goods. The year ended with the arrest of Huawei's chief financial officer in Canada at U.S. request, to the consternation of China.
U.S. officials have grown increasingly exasperated about what they see as Germany's naivety about potential Chinese security threats.
(Reporting by Andrea Shalal in Berlin and Diane Bartz in Washington; Editing by Joseph Nasr and Catherine Evans)