President Donald Trump has declared a national emergency to protect US computer networks from “foreign adversaries”.
The president signed an executive order effectively barring US companies from using foreign telecoms believed to pose a security risk to the country.
Mr Trump does not name any company specifically in the order.
However, analysts suggest it is mainly directed at Chinese telecommunications giant Huawei.
A number of countries have raised concerns the company’s products could be used by China for surveillance.
The Chinese company – which is the world’s largest maker of telecoms equipment – has denied that its work poses any risks of espionage or sabotage.
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According to a statement from the White House, Mr Trump’s order aims to “protect America from foreign adversaries who are actively and increasingly creating and exploiting vulnerabilities in information and communications technology infrastructure and services”.
It gives the secretary of commerce the power to “prohibit transactions posing an unacceptable risk to the national security”, the statement adds.