Rifts grew between the United States and its closest allies on Wednesday as Britain and other European governments refused to back its claim that Iran is planning to mount attacks against US and allied assets in Syria and Iraq.
The US State department said it was withdrawing all non-emergency staff from diplomatic missions in Iraq following warnings from Donald Trump's government about a threat from Iranian-backed militia groups there.
But in a sign of growing differences, the Foreign Office said it had no plans to follow suit and the ministry of defence defended a British general who appeared to question the Trump administration's claims that an imminent threat has emerged from Iran and militias that it backs in recent days.
John Bolton, Mr Trump's national security advisor, announced last week that the US would send an aircraft carrier, 5-52 bombers and a missile battery to the Middle East because of a sudden escalation of that threat. The Pentagon has reportedly drawn up contingency plans for conflict including the deployment of 120,000 troops.
Maj Gen Chris Ghika, the deputy commander of Operation Inherent Resolve, the US-led coalition fighting Islamic State in Syria and Iraq, told reporters in a conference call on Monday: "No, there's been no increased threat from Iranian-backed forces in Iraq and Syria."
Hours later US Central Command, which is responsible for US military operations in the Middle East, took the unusual step of publicly contradicting him.
"Recent comments from OIR's Deputy Commander run counter to identified credible threats available to intelligence from US and allies regarding Iranian-backed forces in the region," said Captain Bill Urban, a spokesman, in a statement.
The ministry of defence said on Wednesday that Maj Gen Ghika was speaking only as an officer focused on the fight against Isil and that he had been clear that threats to US and allied forces do indeed exist.
But it avoided endorsing the US assessment that the threat level has recently increased, saying only that Britain had long-standing concerns about Iran's role in the region.
The incident reflects diplomatic dilemmas. While British officials may be uneasy about US rhetoric towards Iran, they will be wary of jeopardising the UK's single most important security relationship by alienating the Trump administration.
Although Germany and the Netherlands said they would halt military training programs in Kurdish-controlled northern Iraq for security reasons, Jens Flosdorff, a spokesman for the German defence ministry, also said there was "no concrete threat" and that training may resume in several days.
France said it had no plans to withdraw diplomats or suspend its own military training programs.