Speaking to Sky News, Taliban spokesperson Dr Suhail Shaheen said 31 August, the original date set by US President Joe Biden for the completion of the drawdown, is a "red line".
"So if they extend it that means they are extending occupation while there is no need for that," he said.
"If the US or UK were to seek additional time to continue evacuations – the answer is no. Or there would be consequences.
"It will create mistrust between us. If they are intent on continuing the occupation it will provoke a reaction."
It comes as Prime Minister Boris Johnson is expected to use an emergency G7 summit to follow up on the UK's push for President Biden to extend the Kabul evacuation deadline.
Watch: Former interpreter's family suffering for 'British Army' work in Afghanistan.
According to multiple reports, the Prime Minister is due to use the meeting to personally lobby Mr Biden on the issue.
In a tweet, Mr Johnson said it was "vital that the international community works together to ensure safe evacuations".
This follows the UK's Foreign Secretary Dominic Raab and Defence Secretary Ben Wallace holding talks with their US counterparts over the weekend to make clear the desire for US troops to remain in Afghanistan beyond 31 August.
This is so the operation to get British Nationals and former Afghan staff out of the country can continue.
Watch: Former Royal Marine – UK and US responsible for 'absolute carnage' at Kabul airport.
Foreign Office minister James Cleverly told the BBC the Government would continue to try to convince the White House incumbent to extend the exit deadline.
"Obviously the more time that we've got, the more people we can evacuate and that's what we're pushing for," said Mr Cleverly.
However, Mr Biden signalled on Sunday that he did not want US armed forces to stay in Afghanistan beyond August.
When asked about delaying the withdrawal of US troops during a press conference, Mr Biden said the "hope is that we don't have to extend but there are discussions going on about how far we are."
Mr Biden also said he thought US efforts to rescue American citizens from Afghanistan could wrap up at the end of the month.
Cover image: ALAMY.