The US government warned the UK that its approach to building 5G networks could put national security at risk, after an intelligence agency appeared to downplay the threat posed by Chinese vendor Huawei.

Financial Times (FT) reported that members of US President Donald Trump’s administration have said the UK’s plans to test equipment made by the Chinese vendor before it is installed will not be sufficient to safeguard future telecoms networks.

The US continues to pressure its allies to ban Huawei and ZTE from participating in nationwide 5G rollouts, as it believes equipment made by the vendors contains backdoors allowing spying by the Chinese state.

Its latest warning appears to be a response to comments made by UK’s National Cyber Security Centre (NCSC), which said last month it did not believe banning Huawei equipment from 5G rollouts was warranted.

An NCSC representative told Mobile World Live it has concerns around Huawei equipment and detailed improvements it expects the company to make. But it remained unconvinced that it needed to ban the vendor.

The UK government is currently reviewing whether Huawei can be used in 5G networks, which is expected to be published by April.

FT quoted a senior US official as stating that the UK’s approach to testing telecoms equipment in past networks had been sufficient. However, 5G is based on software, meaning it differs from other mobile technology as it can be altered after being tested.

Commenting directly on the NCSC, which tests Huawei equipment in the UK, the source said: “The mandate that the UK and their Huawei oversight centre…is purely a technical mandate about looking at a piece of equipment that is sitting in front of you. Ours is a much broader question about how trust is changing in the way in which 5G networks will work in the future. Right now, backdoors exist by definition, that’s how the manufacturer runs the network.”

The US’ comments to the UK followed a threat to cut back on intelligence sharing with Germany if Chinese vendors are allowed to participate in the country’s 5G rollout.