The top British general in the US-led coalition against Isis has said there is no increased threat from Iranian-backed forces in Iraq or Syria, directly contradicting US assertions used to justify a military buildup in the region.

Hours later however, his assessment was disowned by US Central Command in an extraordinary rebuke of an allied senior officer. A spokesman insisted that the troops in Iraq and Syria were on a high level of alert due to the alleged Iranian threat. The conflicting versions of the reality on the ground added to the confusion and mixed signals in a tense part of the Middle East.

Maj Gen Christopher Ghika, who is a deputy commander of Operation Inherent Resolve (OIR), the coalition conducting counter-terrorist operations against Isis in Iraq and Syria, was repeatedly questioned by reporters about the threat from Shia militias in Syria and Iraq, cited by US officials over the past week as justification for speeding up the deployment of an aircraft carrier strike group in the Gulf and for sending B-52 Stratofortress bombers and an anti-aircraft battery to the region.

“No – there’s been no increased threat from Iranian-backed forces in Iraq and Syria,” Ghika said in a videolink briefing from Baghdad to the Pentagon. “We’re aware of that presence, clearly. And we monitor them along with a whole range of others because that’s the environment we’re in. We are monitoring the Shia militia groups. I think you’re referring to carefully and if the threat level seems to go up then we’ll raise our force protection measures accordingly.”

On Tuesday night, US Central Command – whose area of operations covers the Middle East and Afghanistan – put out a statement refuting Ghika’s comments.

“Recent comments from OIR’s deputy commander run counter to the identified credible threats available to intelligence from US and allies regarding Iranian-backed forces in the region,” it said.

“US Central Command, in coordination with OIR, has increased the force posture level for all service members assigned to OIR in Iraq and Syria. As a result, OIR is now at a high level of alert as we continue to closely monitor credible and possibly imminent threats to US forces in Iraq.”

The rebuke was particularly striking as it implied that Ghika was unaware of the state of alert of his own troops. The remarkable comments heightened concerns that fabricated or exaggerated intelligence may be being used by administration hawks led by the national security adviser, John Bolton, to further the case for war against Iran, in a manner reminiscent of the buildup to the Iraq invasion.

The New York Times reported on Monday night that the acting defence secretary, Patrick Shanahan, had presented the White House with a plan that involved sending up to 120,000 troops to the Middle East in the event of an Iranian attack or departure from the constraints of the 2015 nuclear deal that the US abrogated a year ago.

The revised plans were ordered by administration hardliners led by Bolton, the report said.

Donald Trump dismissed the account as “fake news” on Tuesday. “Now, would I do that? Absolutely. But we have not planned for that,” the president said. “Hopefully we’re not going to have to plan for that and if we did that, we’d send a hell of a lot more troops than that.”

US officials have said there was clear evidence that Iran was building up its proxy forces’ combat readiness and preparing them to attack US forces in the region. The secretary of state, Mike Pompeo, went to Brussels on Monday to brief his European counterparts on the alleged threats.

Speaking in Russia on Tuesday, Pompeo said the United States does not want war with Iran but vowed to keep pressuring Tehran.

“We fundamentally do not seek a war with Iran,” he said, adding: “We have also made clear to the Iranians that if American interests are attacked, we will most certainly respond in an appropriate fashion.”

The Shia militias in Iraq are collectively known as the Popular Mobilisation Forces (PMF), and have ties of varying strengths to Iran.

In his briefing from Baghdad on Tuesday, Ghika told Pentagon reporters: “We’ve seen no change in the posture or the laydown of the PMF. And of course the PMF is a moniker for a very broad range of groups. So I think it’s important to say that many of them are compliant and we have seen no change in that posture since the recent exchange between the United States and Iran. And we hope and expect that that will continue.”

The general stressed that the coalition’s mission was exclusively focused on defeating the remains of Isis and not on confronting Iran, but he added that the issue of force protection had been reviewed “in the light of the events of the last week or so”.

“Am I concerned about the danger? No, not really,” Ghika said.

Saudi Arabia said on Tuesday that armed drones had attacked two of its oil pumping stations, two days after two Saudi oil tankers were sabotaged off the coast of the United Arab Emirates.

The Saudi energy minister, Khalid al-Falih, said that the alleged drone attacks caused a fire and minor damage to one pumping station, and implied that the drone strikes and the sabotage of the tankers were the work of Iranian proxies.

“These attacks prove again that it is important for us to face terrorist entities, including the Houthi militias in Yemen that are backed by Iran,” Falih said in an English-language statement issued by his ministry.

Iran’s ambassador to the UN, Majid Takht Ravanchi, denied any involvement by his country or any of its regional allies in the attacks.

“Definitely not,” Ravanchi told CNN. “Iran is not in the business of doing such a thing. We need to have a thorough investigation as to what has happened and who is responsible for it.”

Pompeo’s briefing to European foreign ministers in Brussels reportedly failed to convince them of the urgency of the Iranian threat. They repeated their commitment to the 2015 nuclear deal, and warned of the dangers of unintended consequences of a military build-up.

Spain announced on Tuesday that it had withdrawn a frigate from a US-led naval group in the Gulf on the grounds that it had changed its mission from celebrating 500 years of the first circumnavigation of the globe, to focusing on alleged threats from Iran.

Additional reporting by Patrick Wintour