© Provided by The GuardianPhotograph: Philipp Guelland/EPA
The US defence secretary, Mark Esper, warned that US alliances including the future of Nato were in jeopardy if European countries went ahead with using Chinese Huawei technology in their 5G networks.
Esper also warned future intelligence cooperation would be at risk, as the US would no longer be certain its communications networks are secure.
His remarks at the Munich security conference on Saturday, bolstered by similar warnings from the US secretary of state, Mike Pompeo, remove any doubt that the US sees finding an alternative to Huawei as central to its own security.
Esper said he had not looked at the specific proposal in detail, and admitted the US was vulnerable to the charge that it had not produced an alternative to Huawei for Europe.
He said he was willing to work with European partners to see if firms such as Ericsson could develop an alternative, and that Washington is currently working to support the development of alternatives.
"We are encouraging allied and US tech companies to develop alternative 5G solutions and we are working alongside them to test these technologies at our military bases as we speak," he said.
"Developing our own secure 5G networks will outweigh any perceived gains from partnering with heavily subsidised Chinese providers that answer to party leadership."
Esper admitted the response to US demands to stay clear of Huawei had been mixed, and said too many countries were focused on short-term economic gain rather than the long-term threat to security.
Lindsey Graham, a US senator close to Donald Trump, also warned the UK risked burning its bridges if it includes Huawei technologies in in its 5G network. He said: "The one thing you need to get is that politics back home is about as screwed up as I have ever seen it. What do we agree on? That Huawei technology is a threat to the US and, we really think, to the world order.
"Nancy Pelosi [the Democrat House speaker] and Donald Trump are not going to have many dinners together, but if you ask them about the British purchase of Huawei they will give you the same answer. We are very firm in our commitment - Republicans and Democrats - that if you go down the Huawei road you are going to burn a lot of bridges."
Pompeo's speech, in which he warned that Chinese officials were trying to infiltrate US networks, came a day after the German president, Frank-Walter Steinmeier, suggested the US rejected "even the idea of an international community" and was acting "at the expense of neighbours and partners".
Pompeo hit back, paraphrasing a famous Mark Twain quote: "Those statements don't reflect reality. I'm happy to report that the death of the transatlantic alliance is grossly overexaggerated." He pointed out that nearly 40 American congressmen and women were attending the conference in a show of transatlantic unity.
Pompeo said Washington played a key role in keeping Europe safe by reinforcing Nato's eastern flank on the border with Russia, and had led a multinational effort to defeat Islamic State group.
"Is this an America that 'rejects the international community'?" he asked. "The free west has a brighter future than illiberal alternatives."
He also warned of the threats posed by Russia's territorial ambitions, China's military buildup in the South China Sea and Iran's "campaigns of terror" through proxy conflicts in the Middle East.
Reflecting US concern over plans to increase European reliance on Russian natural gas through the Nord Stream 2 project, which will pipe Russian gas into Europe, bypassing Ukraine, Pompeo also announced the US would finance energy projects in eastern EU countries.
"The United States - through our International Development Finance Corporation, and with the support of the US Congress - intends to provide up to $1bn in financing to the central and eastern European countries of the Three Seas Initiative."