US Secretary of State Antony Blinken has warned that the Taliban would have to earn legitimacy from the world, after talks with allies on how to present a united front to the hardline new government in Afghanistan.

"The Taliban seek international legitimacy. Any legitimacy -- any support -- will have to be earned," Blinken told reporters at the US airbase in Ramstein, Germany, after leading a 20-nation  ministerial virtual meeting on the Afghan crisis.

A senior State Department official said all countries were broadly on the same page on dealing with the Taliban caretaker government -- including Pakistan, historically the insurgents' ally.

"Pakistan was there. They talked about their unique role, from their perspective... they certainly said that we’re in a position where we have to engage to some degree," the official told reporters on Blinken’s plane.

"But nothing along the lines of, we think we have to recognise or legitimise the government in the near term," he said.

The official said Washington has had no contact, even indirectly, with another key neighbour, Iran, on Afghanistan.

Iran has historically opposed the Taliban but developed relations as the United States, Tehran’s arch-nemesis, carried out its withdrawal.

Pakistan's Foreign Minister Shah Mahmood Qureshi tweeted: "We must not allow creation of a political vacuum in Afghanistan leading to insecurity and instability.

"A stable & peaceful Afghanistan only be achieved through more, not less, regional & int'l engagement.

"Pakistan, as an immediate neighbour cannot afford to disengage," he said.

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German Foreign Minister Heiko Maas noted the international community expected the Taliban to uphold human rights, including those of women, grant access to humanitarian aid and allow those wishing to leave the country to do so.

Maas said he believed Wednesday's talks were "the starting point for international coordination" on how to deal with the Taliban.

Blinken and Maas both criticised the caretaker government announced in Afghanistan on Tuesday, which has no women or non-Taliban members and includes an interior minister the United States wants to arrest on terrorism accusations.

Blinken said the caretaker cabinet would be judged "by its actions".

- Meeting refugees -

Blinken's stop in Ramstein was his second base visit in as many days, after he visited Qatar on Tuesday.

Thanks were offered thanks to US civilian and military officials behind one of history's largest airlifts after Afghanistan fell to the Taliban.

At the entrance to a vast hangar where some of the 11,000 Afghans at Ramstein  await flights to the United States, Blinken showed photos on his telephone of his own children to the four-year-old son of Mustafa Mohammadi, an Afghan military veteran turned refugee who worked with the US embassy.

The stepson of a Holocaust survivor and longtime advocate for refugees, Blinken also toured a makeshift home for some of the children who have lost their parents.

"Many, many, many Americans are really looking forward to welcoming you and having you come to the United States," he said.

Hanging on the walls were artwork by children, including a picture of a girl on a cliff beneath a deep-blue sky with a broken heart and a message in English, "Say to my Mom I miss you."

- Seeking international pressure -

The United States and its allies evacuated some 123,000 people, mostly Afghans who fear Taliban retribution, in the final days of the 20-year US war that President Joe Biden ended last month.

But US officials acknowledge that many more remain and say the Taliban have agreed to let them leave.

Blinken vowed to press the Taliban to allow charter flights out of Afghanistan after criticism the US administration was not doing enough to help those still stranded.

"We are working to do everything in our power to support those flights and to get them off the ground," Blinken said.

Germany, like many US allies, had celebrated Biden's victory over Donald Trump and the new administration's stated emphasis on working with the rest of the world.

But even some close allies have been critical over how Biden ended the 20-year war in Afghanistan, which led to the Western-backed government crumbling within days.

Armin Laschet, the leader of German Chancellor Angela Merkel's ruling party and candidate to succeed her, described the Afghanistan mission as "the biggest debacle" in NATO's history.

Biden has long favoured pulling out of Afghanistan, arguing the US-led NATO mission had achieved its core goal of accountability for the September 11 attacks 20 years ago this week.

Thousands of fighters can return 'anytime': Massoud

Thousands of fighters opposed to the Taliban can return "anytime" in the Panjshir Valley, said the uncle of a commander who led fierce battles against the Islamists, appealing on Tuesday for international support for their cause.

Ahmad Wali Massoud was speaking in Switzerland, one day after the Taliban claimed total control over Afghanistan, declaring that they had won the battle against resistance forces in the mountainous Panjshir Valley, northeast of Kabul.

"We still have thousands of fighters in the valley, and any time they can come back and you will be witnessing that one," Massoud told a symposium in Geneva.

"Yes, we have been wounded and we have been really wounded, but we have not died, we are still alive," he added.

Massoud is brother of the late Ahmad Shah Massoud, the legendary anti-Soviet and anti-Taliban commander assassinated by Al-Qaeda days before the September 11, 2001 attacks on the United States.

Shah Massoud's son, Ahmad Massoud, led resistance to the Taliban in the Panjshir Valley.

On Monday, the Taliban said they had won that battle in what was the last remaining holdout against their rule. They released a video of their flag being raised over the governor's house in Panjshir.

"Panjshir is not only resistance, (it) is a cause, an international cause," Massoud told the symposium.

"We are resisting for our own right, for the freedom, for democracy, for the human rights..."

"Probably this is the last opportunity that we can see to really fight terrorism inside Afghanistan," he added.

"That's why we should not lose the resistance."

The National Resistance Front (NRF) in Panjshir -- made up of anti-Taliban militia and former Afghan security forces -- on Sunday acknowledged suffering major battlefield losses and called for a ceasefire.

But on Monday the group said in a tweet that its fighters were still present in "strategic positions" in the valley.