British sources have said a “joint decision” was taken with the US to keep Kabul airport’s Abbey gate open before last week’s terror attack, in an attempt to dispel a leaked claim from the Pentagon that it was done on behalf of the UK. The effort to smooth over transatlantic differences comes at a time of growing political concern over the US-UK relationship, and in response to an unusually detailed insider account of Pentagon decision-making. On Monday it was claimed that the Americans had kept the gate next to Kabul airport “open longer than they wanted to” to help the British complete the final stages of their evacuation from Kabul. But on Tuesday British defence sources said both countries’ militaries had agreed to keep the Abbey gate open despite the growing terror threat. It was described by the insiders as a “joint decision”. There had been specific warnings that an attack by Islamic State Khorasan Province (ISKP) was imminent and that the Abbey gate used by the British was a likely target. More than 170 Afghans and 13 US marines were killed in a double bomb attack at the gate and the nearby Baron hotel, which was also being used by British officials. Responsibility was claimed by ISKP, the Afghan affiliate of the global terror group. The US website Politico reported on the US military’s thinking in the run-up to Thursday’s attack, saying senior officials in Washington discussed on Wednesday how to prepare for what they feared was an imminent “mass casualty event”. Commanders had concluded that the Abbey gate was potentially the highest-risk location, where crowds had massed in the hope of being able to travel to the west. According to notes of meetings obtained as part of the leak, R Adm Peter Vasely, the commander of US forces in Afghanistan, told senior colleagues that the Abbey gate was not closed on Thursday afternoon Kabul time as had been planned. If accurate, that would imply the decision was not necessarily consensual, as the new British account suggests. Tobias Ellwood, the chair of the House of Commons defence select committee, said the apparent blame game suggested that US-UK relations were at a low ebb. “There’s big questions to do with the back channels and the communications and the bonds that we have with our closest security ally: they were not functioning as they should do,” the MP said. “I’ve been speaking to my colleagues and friends on both sides of the aisle in Washington DC, and there’s agreement that it’s highlighted how weak what has traditionally been a very strong bond has become.” The Labour MP Neil Coyle, a member of the foreign affairs select committee that will put questions to Dominic Raab, the foreign secretary, on Wednesday, said answers were needed about what the UK had done to try to understand and influence the White House. “What was the ambassador in Washington saying? What was being said at the UN? What was being done at Nato?” he said. “Why has ‘global Britain’ been ignored?” Earlier on Tuesday Raab rejected US claims that Britain was indirectly responsible for the suicide attacks at Kabul airport. He told the BBC the “story was simply untrue”, adding that nothing the UK was doing required the Abbey gate to be kept open that day. “We coordinated very closely with the US, in particular around the [ISKP] threat, which we anticipated although tragically were not able to prevent, but it is certainly right to say we got our civilians out of the processing centre by Abbey gate, but it is just not true to suggest that other than securing our civilians inside the airport that we were pushing to leave the gate open,” he said. On Monday the UK briefed that it had nothing substantive to say about the Politico report. Raab’s statement and the revised briefing demonstrate that UK politicians and the military recognised that the seriousness of the story required them to provide a fuller version of events.