The UK will allow China's Huawei a limited role in building the country's 5G network, the government has announced.

In a long-awaited decision, which comes three days before Brexit, Prime Minister Boris Johnson gave the go-ahead on Tuesday but with restrictions on "high-risk vendors" who would be denied access to the sensitive core of networks and have a 35 percent cap on their involvement in the non-sensitive parts.

While refraining from naming Huawei directly, the UK government statement said "high-risk vendors" would be excluded from all critical networks and sensitive locations, such as nuclear sites and military bases.

Johnson chaired a meeting of the National Security Council, where it was agreed that the National Cyber Security Centre should issue guidance to UK telecoms operators.

Digital Secretary Baroness Morgan said: "We want world-class connectivity as soon as possible but this must not be at the expense of our national security. High risk vendors never have been, and never will be, in our most sensitive networks.

"The government has reviewed the supply chain for telecoms networks and concluded today it is necessary to have tight restrictions on the presence of high-risk vendors."

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The British government's announcement came despite warnings from Washington against allowing a role for Huawei.

A Trump administration official has said that the U.S. "is disappointed" with the decision taken by its close ally.

President Donald Trump wanted Britain to impose a blanket ban on Huawei, claiming that Beijing could use the company's equipment to steal Western secrets.

The U.S. president and the UK prime minister spoke on Tuesday afternoon about the decision - the White House said they "discussed critical regional and bilateral issues, including telecommunications security."

Newt Gingrich, a former speaker of the U.S. House of Representatives rued the White House's current policy.

"British decision to accept Huawei for 5G is a major defeat for the United (States). How big does Huawei have to get and how many countries have to sign with Huawei for the U.S. government to realize we are losing the internet to China? This is becoming an enormous strategic defeat."

The U.S. has argued that with 5G evolving, the distinction between the "edge" and "core" will gradually dissipate as data is processed through the network, increasing risks of malicious breach and theft.

^{CGTN Europe's Nawied Jabarkhyl explains the issues}

Huawei, which has consistently denied charges of espionage, points to its competitive pricing as the reason for U.S. resistance over the telecom giant's entry into the UK's 5G network.

Victor Zhang, vice-president of Huawei, said: "We have supplied cutting-edge technology to telecoms operators in the UK for more than 15 years. 

"We will build on this strong track record, supporting our customers as they invest in their 5G networks, boosting economic growth and helping the UK continue to compete globally.

"We agree a diverse vendor market and fair competition are essential for network reliability and innovation, as well as ensuring consumers have access to the best possible technology."

Huawei hardware is already being used by some of Britain's biggest telecoms providers, including BT and Vodafone. The equipment, though, has been deployed at the periphery of the network, separated from the "core" where data is processed.

^{Huawei UK vice president Jeremy Thompson explains what role the company has in the UK 5G network}