US and other allied troops were struggling to reopen Kabul airport on Monday after seven people were killed in chaotic scenes as desperate civilians converged on the only route out of the capital in the aftermath of the Taliban’s seizure of Kabul.

A day after the group took control of the city, declaring victory after 20 years of war, tens of thousands of Afghans who have been promised resettlement in the west because of their past work with the US, Britain and their allies, remained trapped in the country and in fear for their lives, amid reports of reprisal killings.

In Kabul and cities across the country, Taliban forces asserted control ahead of an expected announcement of an Islamic Emirate of Afghanistan in the coming days.

With Kabul airport seemingly close to being overrun, flights were grounded and several people died. Two were killed when they fell from a US military plane that they had tried to cling to as it took off from Kabul. Others appear to have died in the crush on the tarmac.

The US announced it was sending another 1,000 troops to help with the evacuation, and the British another 200.

But video footage of scores of Afghan civilians running alongside the US transporter plane as it taxied through them is likely to haunt Joe Biden, who is reported to have been anxious to avoid echoes of the hurried US escape from Saigon 46 years ago, even as he ordered the total withdrawal from Afghanistan by 11 September.

The UK defence secretary, Ben Wallace, admitted that, as Britain sought to evacuate its own Afghan allies, “some people will not get back”. UK government officials suggested that western capitals only had until the end of August, when the US military mission is formally due to end, to help Afghans leave the country.

In Germany, the chancellor, Angela Merkel, told a meeting of her party that the decision to withdraw was “ultimately made by the Americans” with “domestic political reasons” partly to blame. She said Germany must urgently evacuate up to 10,000 people from Afghanistan for whom it has responsibility, including 2,500 Afghan support staff as well as human rights activists, lawyers and others whom the government sees as being at risk.

Biden was due to return to Washington from Camp David to make a statement about Afghanistan, amid bitter criticism of the speed and handling of the departure.

The Pentagon confirmed the head of US Central Command, Gen Kenneth McKenzie, met Taliban officials in Doha on Sunday, as Kabul was falling, to hold talks about security in the capital during the US evacuation effort.

“The general was very clear and firm in his discussions with Taliban leaders that any attack on our people … would be met with a very swift and forceful response,” the Pentagon spokesman, John Kirby, said.

Kirby confirmed that US troops had shot and killed two gunmen who had opened fire on a crowd of thousands of Afghan civilians who had rushed on to the Kabul airport tarmac in the hope of finding a flight out.

“It’s our understanding that these troops acted on what was perceived to be a real and tangible threat,” the defence department spokesman said, adding there was no evidence that the gunmen were Taliban.

Kirby said US, Turkish and other allied troops were working to clear the runways on Monday. There are currently 2,500 US troops at the airport, where the US embassy has temporarily re-established itself since the Taliban takeover, and a further 3,500 are due to fly in when the runways are open.

The Taliban leaders have offered assurances that there will be no reprisals against Afghans seen as having cooperated with westerners since 2001, but the Afghan ambassador to the United Nations told the security council that in Kabul, the Taliban were already “going house to house looking for people on their target list”.

“Today I’m speaking on behalf of millions of people in Afghanistan, whose fate hangs in the balance and are faced with an extremely uncertain future,” Ghulam Isaczai, who had been in the post less than a month before his government fell, told the council.

“We’re extremely concerned about Taliban’s not honouring the promises and commitments made in their statements at Doha, and other international fora,” Isaczai said.

“We’ve witnessed time and again how the Taliban have broken their promises and commitments in the past. We have seen gruesome images of Taliban mass executions of military personnel and targeted killings of civilians in Kandahar and other big cities.”

The Uzbek government said on Monday its forces had shot down an Afghan air force jet and had forced other Afghan planes to land, but it was not immediately clear if the incidents reflected an attempt by the air force to escape Taliban capture. The Taliban had carried out a campaign of assassination of Afghan pilots.

At Monday’s emergency security council meeting on Afghanistan, the UN secretary general, Antonio Guterres, said the fate of the Afghan people was in the balance.

“The following days will be pivotal. The world is watching,” Guterres said. He said that so far UN staff and offices have not been harassed by the Taliban and the UN coordinator in Kabul, Ramiz Alakbarov, said his office would work with the “de facto authorities” to provide humanitarian assistance, telling the Associated Press that the upsurge in fighting that led to the fall of Afghanistan’s provincial capitals to the Taliban had displaced 600,000 people.

At the security council meeting, Russia and China expressed willingness to work with the Taliban.

“There is no point in panicking,” the Russian permanent representative, Vasily Nebenzya, said. “We urge all Afghan parties to foster a settlement peacefully. A bloodbath has been avoided.”

The Chinese foreign ministry indicated on Monday it was willing to recognise the Taliban regime, but Moscow said it would first monitor its behaviour in its early days back in power.

The US ambassador, Linda Thomas-Greenfield, said the US “promises to be generous in resettling Afghans in our own country” – a claim which followed severe criticism at the slow pace of processing visas for interpreters and other former employees.

After trying to negotiate agreements with countries in the region to accept Afghan civilians while their visas were being processed, there were reports that the Biden administration would bow to pressure from refugee advocates and fly them to the US for vetting.

Fox News reported that Fort McCoy in Wisconsin and Fort Bliss in Texas were being considered as the initial venues for accepting the first of potentially tens of thousands of Afghan refugees.