US National Security Adviser Robert O’Brien has warned Britain about allowing China’s Huawei company into its 5G telecommunications networks, saying such a move would pose a risk to UK’s secret intelligence agencies, according to British media.

In an interview with the Financial Times published on Tuesday, O’Brien said that people in Europe, Japan, Australia and New Zealand were beginning to realize concerns raised by Washington against Huawei.

They are just going to steal wholesale state secrets, whether they are the UK’s nuclear secrets or secrets from MI6 or MI5, O’Brien told the FT.

It is somewhat shocking to us that folks in the UK would look at Huawei as some sort of a commercial decision. 5G is a national security decision, he added.

The administration of US President Donald Trump has been pressing allies to exclude Huawei from their 5G networks over fears the company could spy on customers for Beijing, which the Chinese firm has repeatedly denied.

Citing national security concerns, the Trump administration placed the company on a trade blacklist in May, preventing companies that make products in the United States from selling to Huawei without a special license.

The US Commerce Department is considering toughening export restrictions on the firm, which is the world’s second largest smartphone supplier.

Britain has previously taken a softer line compared to other countries in the Five Eyes intelligence-sharing network, indicating Huawei’s 5G products could be used in less sensitive areas. The Five Eyes intelligence-sharing network includes the United States, UK, Canada, Australia and New Zealand.