UPDATE 2-Not clear UK has made final decision on Huawei -U.S. national security adviser Bolton

U.S. President Donald Trump's national security adviser John Bolton said on Thursday it was not clear to the United States that a decision on British government policy towards Chinese telecoms firm Huawei had been taken in its final form. He said Huawei technology could allow "back doors" into telecoms systems and contested the British view that new 5G networks could be separated into core and peripheral systems.

The United States is worried that 5G dominance would give any global competitor such as China an advantage Washington is not ready to accept. But British ministers have discussed allowing Huawei a restricted role in building parts of its network.

"I'm not sure that this decision has reached the prime ministerial level in final form. I mean we are still talking ... people are talking back and forth," Bolton told reporters in London. "I think everybody is catching up to the dangers posed, especially in 5th-generation telecommunications systems, by equipment from Huawei and potentially others that can allow foreign governments a back door into telecommunications systems."

Britain has said it will announce the findings of a review into 5G suppliers to parliament once the work has been completed. It has not yet set out a timeline for this. Britain's political crisis over Brexit, Prime Minister Theresa May's planned resignation, and the contest to replace her could all complicate the announcement of any decision.

Bolton said the issue came down to a risk assessment. "How much risk are you prepared to accept that a foreign power is reading your mail all the time at their will? When it comes to our government systems, the United States has said zero is the level of risk we will accept."

He said that led to questions about what type of communications between government systems would be possible in the future. "That is what we are trying to explain to all of our partners," he said.