Western countries have sped up evacuations from Afghanistan in recent days, after the Taliban said it would not agree to extend the Aug 31 deadline for the full withdrawal of US troops.

A NATO official quoted by Reuters, who declined to be identified, said that every member of foreign forces in Afghanistan "is working at a war-footing pace to meet the deadline".

About 50,000 foreigners and Afghans have fled the country from Kabul's international airport since the Taliban swept to power on Aug 15, according to the United States government. On Tuesday, the US military ramped up efforts to airlift thousands of people out of Kabul. France said it will end its evacuations later this week if the US still plans to pull its troops out at the end of August.

Taliban spokesman Suhail Shaheen said an extension of the withdrawal deadline was not acceptable.

"You can say it's a red line," he said in an interview on Monday with Sky News. "President Biden announced this agreement, that on the 31st of August they would withdraw all their military forces. So if they extend it, that means they are extending occupation," he said, adding such a move would deteriorate relations and create mistrust.

"If they are intent on continuing the occupation … it will provoke a reaction," he said.

Leaders of the Group of Seven countries－Britain, Canada, France, Germany, Italy, Japan and the United States－were scheduled to have an online meeting on Tuesday to discuss the crisis.

British officials said UK Prime Minister Boris Johnson will use the emergency meeting to propose new sanctions on the Taliban and try to persuade US President Joe Biden to extend the evacuation operations, according to the Washington Post.

China's Foreign Ministry spokesman Wang Wenbin said on Tuesday that more sanctions and pressure will not solve the problem and only prove to be counterproductive.

"The international community should encourage and promote the development of the situation in Afghanistan in a positive direction, support the peaceful reconstruction of Afghanistan, improve people's livelihoods and well-being, and enhance the capacity for independent development," Wang said at a news briefing in Beijing.

He said the US and its allies should learn from history and act cautiously, and the international community should not again pay the bill owed by certain countries.

Biden, who has said US troops might stay beyond the deadline, has warned the evacuation is going to be "hard and painful" and much could still go wrong.

Kabul's international airport, from which the evacuation flights arrive and leave, has witnessed chaotic scenes. Tens of thousands of people have flocked to the airport, which has seen sporadic outbreaks of violence.

Adam Schiff, chairman of the US House of Representatives' Intelligence Committee, said after a briefing on Afghanistan by intelligence officials on Monday that he did not believe the evacuation could be completed in the eight days remaining. "I think it's possible, but I think it's very unlikely given the number of Americans who still need to be evacuated," Schiff said.

UK Defence Secretary Ben Wallace said that the United Kingdom, like other nations dependent on US air and ground support in Afghanistan, will have to halt its evacuation efforts when US forces leave.

"It's really important for people to understand the United States has over 6,000 people in Kabul airport, and when they withdraw, that will take away the framework … and we will have to go as well," Wallace said.

Britain said it has evacuated 8,600 UK citizens and Afghans from Kabul in recent days, including 2,000 in just 24 hours. But Wallace conceded that "we're not going to get everybody out of the country".