US President Donald Trump has criticised the UK ambassador who said in leaked emails that his administration was "inept".
Mr Trump said: "The ambassador has not served the UK well, I can tell you that."
Emails from Sir Kim Darroch said Mr Trump's White House was "uniquely dysfunctional" and "divided".
Trade secretary Liam Fox told the BBC the leak was "unprofessional, unethical and unpatriotic".
He said that whoever released the emails had "maliciously" undermined the defence and security relationship with the US, "the most important global relationship that we have".
"I hope if we can identify the individual, either the full force of internal discipline - or if necessary the law - will be brought to bear because this sort of behaviour has no place in public life," he said.
As the Foreign Office launched an investigation into the source of the leak to the Mail on Sunday, Mr Trump told reporters in New Jersey: "We're not big fans of that man and he has not served the UK well.
"So I can understand it and I can say things about him but I won't bother."
Who is Sir Kim Darroch?
Sir Kim is the British ambassador to the US, which means he represents the Queen and UK government interests in the US.
Born in South Stanley, County Durham in 1954, he attended Durham University where he read zoology.
During a 42-year diplomatic career, he has specialised in national security issues and European Union policy.
In 2007, Sir Kim served in Brussels as UK permanent representative to the EU.
