Donald Trump has declared a “national emergency” as his administration imposed severe sanctions on Chinese telecoms giant Huawei.
The president signed an executive order which – while it did not name Huawei – bars US companies from using telecommunications equipment made by firms deemed to pose a national security risk.
Hours later, the administration took further separate action as the commerce department added Huawei and 70 affiliated companies to a blacklist banning it from acquiring components and technology from US firms without government approval.
Commerce secretary Wilbur Ross said Mr Trump backed the decision that will “prevent American technology from being used by foreign-owned entities in ways that potentially undermine US national security or foreign policy interests”.
Kevin Wolf, a former trade official in the Obama administration, said Huawei would be the largest business ever subjected to such controls.
He said they would have “ripple effects through the entire global telecommunications network”.
“Huawei affiliates all over the planet depend on US content to function and if they can’t get the widget or part of the software update to keep functioning then those systems go down,” Mr Wolf said.
US officials have previously labelled Huawei a threat and lobbied allies not to use its equipment in the development of new 5G mobile networks.
Huawei, which denies its products pose a security threat, said it was “ready and willing to engage with the US government and come up with effective measures to ensure product security”.
A Chinese government spokesman said national security “should not be abused, and that it should not be used as a tool for trade protectionism”.
He added: “China will take all the necessary measures to resolutely safeguard the legitimate rights of Chinese firms.”
Huawei has attempted to calm security fears over its technology by offering to sign “non-spying” agreements – including with the UK government.
The company’s executive vice president Jeremy Thompson this week told Sky’s Ian King that it was willing to go the “extra mile” to reassure countries that it posed last month.
Sources confirmed last month that the National Security Council, chaired by Theresa May, had backed the use of Huawei technology in “non-core” 5G network infrastructure.
That was despite a warning from the National Cyber Security Centre (NCSC) and the US government that the company posed a threat.
While Huawei has always denied a link to espionage, it has a legal obligation to cooperate with China’s intelligence agencies.
The company says information has never been requested about its customers from the Chinese state and its founder has insisted he would rather shut down Huawei than accept any request to collect intelligence via its systems.
The issue of trust in the firm’s links to the Chinese government has become a wider issue for companies across China as the country’s trade war with the US escalates.
Washington accuses Beijing of intellectual property theft and forced transfers of technology.