The United Nations has said it is bracing for a possible exodus from violence-ravaged Afghanistan of up to half a million more refugees by the end of 2021.

The organisation said that there currently was not a flood of people fleeing across Afghanistan's borders, but added it was laying contingency plans for that to change as the country's crisis deepens.

"The humanitarian emergency currently is inside Afghanistan," Kelly Clements, the deputy high commissioner of the UNHCR, told reporters.

"This is obviously a really dynamic situation," she said, explaining that the UNHCR was planning for a variety of different scenarios, including a mass-exodus.

"We are preparing for around 500,000 new refugees in the region. This is a worst-case scenario," she said.

She stressed in particular the need to boost support for neighbouring countries that already host the more than 2.2 million Afghan refugees, and which could soon see the fresh influx.

Even before the Taliban swept into power in Afghanistan nearly two weeks ago, the humanitarian situation in the country had deteriorated dramatically.

Half of the population was already in need of humanitarian assistance, and half of all children under five were estimated to be acutely malnourished.

A surge in violence since the start of the year has also prompted nearly 560,000 Afghans to flee within the country, joining some 2.9 million internally displaced people already registered in Afghanistan at the end of 2020, the UNHCR said.

More than 80% of those displaced in 2021 have been women and children.

It comes as the World Health Organization seeks to establish an air bridge into the northern city of Mazar-i-Sharif with the help of Pakistani authorities as medical supplies are due to run out within days in Afghanistan.

The WHO's regional emergency director, Rick Brennan, described the needs as "enormous and growing".

Trauma kits and emergency supplies for hospitals, as well as medicines for treating chronic malnutrition among children are among priority items.

At least one so-called Islamic State suicide bomber killed 85 people, including 13 US soldiers, outside the gates of Kabul airport in twin blasts yesterday evening.

"Right now because of security concerns and several other operational considerations, Kabul airport is not going to be an option for the next week at least," Mr Brennan, speaking from Cairo, told a UN briefing in Geneva.

"One of the problems we have in Afghanistan right now is there is no civil aviation authority functioning but we are working with Pakistan particularly in the context of Mazar-i-Sharif airport. Because they can work with contacts on the ground that all the necessary steps to land an aircraft, to land a cargo aircraft, can be put in place," he said.

Turkey has not made a final decision on a Taliban request for support to run the Kabul airport after foreign forces withdraw over security concerns and uncertainty in Afghanistan, President Tayyip Erdogan said, adding talks were still under way.

Insurance rates for flying into Afghanistan have "skyrocketed at prices we have never seen before", Mr Brennan said.

"So we are trying to jump through that hoop at the moment and once we have addressed that we will hopefully be airborne in the next 48 to 72 hours."

Displaced Afghan families seek food and shelter

Hundreds of Afghan families who have been camping in searing heat at a Kabul park after the Taliban overran their provinces begged for food and shelter yesterday, the most visible face of a humanitarian crisis unfolding in the war-torn country.

The Taliban's swift takeover of Afghanistan this month, culminating in the capture of Kabul on 15 August, has thrown the country into turmoil.

While thousands of people have crowded the airport to try to flee, many others, like the families in the park, are stuck in limbo, unsure whether it is safer to try to go home or stay where they are.

"I'm in a bad situation," said Zahida Bibi, a housewife, sitting under the blazing sun with her large family. "My head hurts. I feel very bad, there is nothing in my stomach."

Ahmed Waseem, displaced from northern Afghanistan said those in the park were hoping the central government would pay attention.

"We are in an open field and in the heat," he said.

A Taliban spokesman told Reuters the group was not providing food to the people at the park and others at the airport because it would lead to further overcrowding.

They should return to their homes, he said.

Afghanistan's western-backed president and many other officials fled after government forces melted away in the face of the Taliban advance.

The group has placed its members in ministries and ordered some officials back to work but services are yet to resume, with banks still closed.

Phalwan Sameer, also from northern Afghanistan, said his family came to Kabul after the situation rapidly deteriorated in his home town.

"There (was) a lot of fighting and bombing as well. That's why we came here. The houses were burned and we became homeless," he said.

The WHO said on Tuesday it has only enough medical supplies in Afghanistan to last a week after deliveries were blocked by restrictions at Kabul airport and the UN World Food Programme said the country urgently needed $200 million in food aid.

The United Nations says more than 18 million people – over half of Afghanistan's population - require aid and half of all Afghan children under the age of five already suffer from acute malnutrition amid the second drought in four years.

The Taliban have assured the UN that it can pursue humanitarian work as foreign governments weigh the issue of whether and how to support the population under hardline Islamist rule.