Trump “just called me from [Air Force One] and instructed me to make clear that any nation who chooses to use an untrustworthy 5G vendor will jeopardise our ability to share intelligence and information at the highest level,” Grenell wrote on Twitter on Sunday.

Similar pressure on the UK, however, did not stop the government from last month allowing Huawei a maximum of 35 per cent share in the non-sensitive parts of its 5G infrastructure, while US Secretary of State Mike Pompeo ruled out any changes to intelligence sharing between Washington and London.

The US president’s threat came as Germany considered how to proceed with its 5G plans. Merkel faces resistance from cabinet members on a proposal to let telecoms companies choose their 5G suppliers.

Huawei slams new US claims of IP theft as ‘political persecution’

European states, while sceptical of US pressure, value the role of Nato after a 70-year period of Cold War with the Soviet Union and turbulent relations with Russia.

The Chinese government has asked the European Union to give Huawei a level playing field. The company, which has repeatedly denied any US allegations, said that its technology was years ahead of major competitors such as Ericsson and Nokia. It also promised to abide by European rules.

For Huawei, the German market, the biggest in the EU, is hugely important.

Merkel has moved cautiously with 5G policy, fearing that any open rejection of Huawei would upset Beijing and lead to economic retaliation against companies such as Siemens and Volkswagen, which have extensive business interests in China.

Under Merkel’s initial plan, German operators such as Deutsche Telekom would have the final say on which 5G suppliers they want to be their partners. The plan would have allowed the US government to put direct pressure on Deutsche Telekom, for instance, as it also runs T Mobile US, the country’s third largest wireless carrier.