Huawei, the Chinese telecoms company, has launched an aggressive counter-offensive against the US government, saying it is high time the US detail “unsubstantiated” national security concerns in the wake of a decision to block the business from building a national emergency communications network.

“Stop the manufactured fear. If you have something to say, substantiate it,” said William Plummer, Huawei’s vice-president of external affairs. The comments represent the most assertive response the company has made since the US began systematically blocking the company from acquiring US assets in 2008.

The group has, in effect, been barred from acquiring two companies over the past four years by the US government, which also intervened in a separate attempt by Huawei to bid for a big contract with Sprint, a big US telecommunications operator. In that instance, according to a person familiar with the matter, the government was also contemplating actions that would have barred Huawei from importing into the US, but stopped short of doing so.