Huawei has been accused of stealing trade secrets and lying to US federal investigators in a new indictment that is likely to deepen US-UK tensions over a recent move by the British government to allow the Chinese company to supply 5G equipment for a new network.

The superseding indictment makes new allegations against the world’s largest telecoms equipment maker, including claims that the company successfully engaged in a decades-long effort to steal intellectual property, giving it an unfair advantage over competitors.

The new indictment also alleges that Huawei engaged in covert efforts to ship its goods and services to Iran and North Korea, in violation of US, European and United Nations sanctions. The Department of Justice said internal documents showed that the company referred to the sanctioned countries using code names, such as “A2” for Iran and “A9” for North Korea, in what prosecutors said reflected the “inherent sensitivity” of this business.

Huawei said in a statement that the new indictment was an attempt to “irrevocably damage Huawei’s reputation and its business for reasons related to competition rather than law enforcement”.

It said: “These new charges are without merit and are based largely on recycled civil disputes from last 20 years that have been previously settled, litigated and in some cases, rejected by federal judges and juries. The government will not prevail on its charges, which we will prove to be both unfounded and unfair.”

The DoJ said its investigation was continuing. It alleged, among other claims, that Huawei had lied about its relationship with Skycom, which prosecutors said was an “unofficial subsidiary” of Huawei that had assisted Iran in performing domestic surveillance, including against demonstrators in Tehran in 2009.

The allegations come a year after the DoJ charged Huawei and Meng Wanzhou, the company’s chief financial officer and the daughter of Huawei’s founder Ren Zhengfei, of fraud and of circumventing sanctions.

Meng was arrested in Vancouver airport in December 2018, and remains on bail in Canada, where she is fighting extradition to the US.

The announcement of new charges in addition to the former criminal accusations comes just weeks after Boris Johnson’s government defied US warnings against Britain’s partnership with Huawei and announced that the Chinese company would serve as a supplier to create a new 5G network.

The British government has sought to limit Huawei’s role. It designated the Chinese company as a “high-risk vendor” and imposed a cap on its involvement in building out the network. Britain’s spy agencies have argued that the risk of using Huawei could be contained, and the government argued in parliament that more was known about Huawei’s risks in Britain than in any other country.

But the indictment presented by the US on Thursday painted a picture of a company that had repeatedly misled attempts to investigate its activities. It described efforts by Huawei to “misappropriate” intellectual property by entering confidentiality agreements with suppliers that were then used by Huawei, and using professors at research institutes to obtain technology.

The indictment also alleges that Huawei “engaged in a pattern of obstruction” to mislead US authorities and advised employees to conceal their employment with the company during encounters with law enforcement officials.