US lobbying against the use of Huawei in British 5G phone networks will step up when the embassy in London hosts an event on Tuesday afternoon to discuss the situation with telecoms companies operating in the UK.

The extraordinary meeting comes a day after an official at the US state department warned publicly that any use of Huawei technology would prompt a reassessment of intelligence sharing with the UK.

Industry sources said the Trump administration wanted to target the mobile phone companies Vodafone, BT and O2, owned by Spanish company Telefonica – although it is not clear who will attend the event.

Such direct lobbying of foreign companies is considered unusual – “it’s a very cheeky thing to do”, said one industry source – but reflects a US determination to prevent Huawei being used at all, in contrast to the proposed British position.

Last week, the UK’s national security council, a meeting of senior ministers and intelligence chiefs, agreed in principle to allow Huawei to supply “non-core” technology in future 5G networks.

The decision was leaked hours after the meeting after five ministers expressed reservations about letting a Chinese company supply strategic technology, reflecting fears that the Chinese government could compromise it in future.

A leak inquiry has begun that could lead to a minister, aide or official being sacked if the culprit is uncovered. People are being called for interview, while phone and email records are being examined.

US officials have been stoking fears about Huawei. Robert Strayer, a deputy assistant secretary at the state department, said on Monday the company “was not a trusted vendor” and that any use of it in British 5G networks was a risk.

He added that the US would have “to reassess the ability for us to share information and be interconnected” if Huawei technology was used.

British intelligence agencies, led by GCHQ, say that the risks from Huawei can be contained, reflecting the decision last week by Theresa May and the national security council to restrict the company to being a non-core supplier in 5G.

The US is also understood to be keen to hear why the mobile phone companies believe they can work with Huawei. The Chinese company has invested heavily in 5G technology and its equipment is considered cheaper than rivals.

A report from the industry body Mobile UK has concluded that cutting Huawei out of the UK 5G network could add an extra £7bn to operator costs.