US Secretary of State Mike Pompeo has urged the UK to prioritise its security interests and those of its allies when dealing with Chinese firm Huawei.
Speaking in London, he said the US had "made its views well known" on Huawei's potential role in the UK's 5G network.
He said the US must protect its UK operations from "security risks" and ensure data partners were "trusted".
Foreign Secretary Jeremy Hunt said the UK would never "compromise" its ability to share intelligence with the US.
Following talks with his US counterpart, Mr Hunt insisted no decision had been taken on whether to involve the Chinese firm in the development of the UK's next generation broadband services, adding that ministers were still "considering the evidence".
The issue caused a major political row last week when defence secretary Gavin Williamson was sacked from cabinet after leaks of discussions from a National Security Council meeting.
This followed media reports suggesting a decision had been taken in principle to award Huawei contracts for non-core elements of the new network.
The US is alarmed at the growing global reach of Huawei, which its critics say is an arm of the Chinese Communist Party and is being used a vehicle to spy on foreign countries.
After talks with Theresa May and Mr Hunt, Mr Pompeo warned of Chinese attempts to "peddle corrupt infrastructure deals in return for political influence" around the world.
Referring to Chinese expansion in East Asia, he urged the UK "to be equally vigilant and vocal against those other Chinese activities which undermine the sovereignty of all nations".
While the UK had the sovereign right to take its own commercial decisions, he indicated the US expected its trusted ally to put security, not financial interests, first.
"I am confident that each of our two nations will choose the path to ensure the security of our networks," he said.
Pressed on the issue, he hinted that the US could re-consider some of its extensive defence and economic interests in the UK if the Huawei deal went ahead.
"We are making our views very well known.
"The US has an obligation to ensure the places where we operate, places where US information is, places where we have national security risks, that they operate within trusted networks and that is what we will do."
Iran and Venezuela
Mr Pompeo said the so-called special relationship between the two countries was "not just enduring but thriving".
But the talks also exposed differences in the two countries' approach to Iran, after Tehran announced it was pulling out of key commitments under the 2015 international nuclear deal.
Last year, President Trump withdrew the US from the multinational accord designed to curb Iran's nuclear ambitions, but the UK and other nations remain signed up to it.
Mr Hunt said Tehran's move was "unwelcome" and while the UK remained committed to a multinational approach to preventing Iran acquiring a nuclear bomb, he said there would be "consequences" for Tehran if it did not reconsider.
Mr Pompeo's first trip to the UK as Secretary of State comes three weeks before US President Donald Trump's own state visit next month.
He said Mr Trump was eager to begin work on negotiating a trade deal with the UK and hoped Britain could resolve the current Brexit stalemate.
He also criticised what he described as some political leaders' "disgusting" support for the regime of Venezuelan leader Nicolas Maduro.
Labour leader Jeremy Corbyn, who has decided to boycott an official banquet for Mr Trump next month, has expressed admiration for the Maduro government in the past.
Unlike other UK politicians, he has not joined calls for the socialist leader to quit following months of social unrest and violence and after the international community recognised opposition leader Juan Gaido as lawful president.