Afghanistan is facing an “absolute catastrophe” involving widespread hunger, homelessness and economic collapse unless an urgent humanitarian effort is agreed in the wake of the US withdrawal, world leaders are warned today.

With growing anger over Britain’s chaotic evacuation effort and people killed in a crush around Kabul airport yesterday, a meeting of G7 leaders has been hastily arranged for early this week. Senior figures in Kabul warned that the latest chaos is combining with drought, huge displacements of people and economic paralysis to create a disaster requiring immediate international action.

Mary-Ellen McGroarty, the UN’s World Food Programme’s country director for Afghanistan, told the Observer that swift coordinated action was critical. “Otherwise, an already horrendous situation is just going to become an absolute catastrophe, a complete humanitarian disaster,” she said. “We need to get supplies into the country, not only in terms of food, but the medical supplies, the shelter supplies. We need money and we need it now.

“Delay for the next six or seven weeks and it’s going to start becoming too late. People have nothing. We have to get food in now and get it to the communities in the provinces, before roads are blocked by snow.”

One of the Taliban’s top leaders, co-founder Mullah Abdul Ghani Baradar, arrived in Kabul for talks with Afghan political leaders including the former President Hamid Karzai, moving the group closer to forming a government, a week after their almost bloodless capture of Kabul.

While some Taliban leaders have promised an inclusive government, and kept figures like the health minister and Kabul mayor in office, one senior figure has ruled out any form of democracy. The meetings come amid continuing chaos and bloodshed at Kabul airport. Many people with links to foreign forces and western organisations do not trust the Taliban’s promises of amnesty.

The troubled evacuation effort was complicated further yesterday when the US embassy warned its citizens to stay away from the airport gates because of security threats. US officials said the most serious risk was an attack by the regional Isis affiliate, the New York Times reported.

It comes with pressure increasing on foreign secretary Dominic Raab over the handling of the evacuation programme, with time running out to complete it. Raab stayed on holiday in Crete last week as Kabul fell to the Taliban. Keir Starmer, the Labour leader, called for him to resign for his failure to make a call to his Afghan counterpart as the government collapsed, but added that Boris Johnson’s response had also been characterised by “complete and utter complacency from start to finish”.

“Raab should definitely go,” he told the Observer. “It is a dereliction of duty – not making the call is the clearest evidence of that. Many Tory MPs know he ought to go. But I also think this reflects on Johnson. There was a time when it would have been obvious that somebody like Raab in this position, given the collapse of the regime in Afghanistan, would have to go. But under Johnson, he doesn’t. There’s a deep sense with the prime minister that time and again, he fails to meet the moment.”

Last night, the Sunday Times reported that Raab was urged by a No 10 official to return from his holiday but stayed for two more days after Boris Johnson allowed him to stay.

Starmer said that he was among many MPs across the country dealing with urgent individual cases of Afghans who have helped British operations trying to secure a flight out of Kabul. He said those eligible for the UK’s refugee system could and should have been processed weeks ago, while the scheme had been drawn too narrowly. Some MPs have complained that a special phone line to report cases has been left unanswered.

MPs on the foreign affairs select committee want to call Raab to an emergency meeting to demand answers about the evacuation. Chris Bryant, a Labour member of the foreign affairs select committee, said: “Nearly every MP is having really distressing phone calls, either from members of the British armed forces or from Afghan families, desperate to save somebody in Afghanistan. We’ve been given a line to ring and it just rings out. Raab must come clean about whether they put enough resources into this, because it feels as if they’re asleep at the wheel.”

Government sources insisted that the UK had engaged in swift diplomacy. Johnson spoke to UN secretary-general Antonio Guterres yesterday and stressed his belief that the UN “must be central to both the humanitarian response to the situation in Afghanistan and international negotiations over the future of the country”.

The UK government is working on tabling a UN security council resolution that can be backed by Russia and China.

Beyond the turmoil around Kabul airport, leaders of the humanitarian effort are deeply concerned about the weeks ahead. Speaking from Kabul, McGroarty said that one in three Afghan people were already in a crisis of hunger, with more than two million children at risk of becoming malnourished. Drought had already led to a 40% reduction in wheat production, while the Afghan currency was collapsing. Covid rates are also high.

“As everybody across the world has been watching, there is the escalation in the conflict over the last couple of months – over 500,000 people displaced, 250,000 of those since May. You saw the tens of thousands of people flowing into Kabul. That has played out right across the country. They have left behind their homes and left behind their farms. People haven’t been able to farm, it’s unsafe to go out.They have nothing but the clothes on their back. What is urgent now is some form of ceasefire that allows a massive scale-up in the humanitarian response. The humanitarian imperative cannot be lost.”

David Miliband, president of the International Rescue Committeeand former foreign secretary, said: “Hours and days matter because everything we know shows that untended humanitarian crisis fuels political instability,” he said. “Anyone who believes that the problems in Afghanistan stay in Afghanistan has got another think coming.”

David Davis, the former Tory cabinet minister, said it was essential the UK now stepped up to meet the humanitarian needs. “If the west wants to be a serious force in the world for the future, it’s vital that we handle at least this part of the exit with a great level of commitment and competence.”

Senior government sources pushed back against suggestions that there was a deadline to complete the evacuation from Kabul, after suggestions that the end of the month could be the fixed end point to military operations.

“We’ve never put a fixed date on withdrawal,” said the source. “The situation on the ground is in flux. Our priority is getting our people out, as safely and as quickly as possible. Obviously the longer the airport is open and secured by western forces, the more room for manoeuvre we have on evacuations.”

In an article published last night, former prime minister Tony Blair, who ordered the UK to join the US-led Afghan invasion in 2001, said the Taliban victory would see “every Jihadist group round the world cheering”.