KABUL: Two powerful explosions outside Kabul airport killed as many as 20 people Thursday, just hours after Western nations warned of an imminent terror threat and thousands of people gathered hoping for a flight out of Taliban-controlled Afghanistan.

The blasts came as the August 31 deadline looms for the United States to withdraw its troops, and for it and other Western countries to end a massive airlift that has already evacuated nearly 100,000 people.

The airport is the only part of the country under foreign control following the Taliban's return to power on August 15, and huge crowds have massed in the hope of being evacuated.

The Taliban condemned the blasts, saying they were in an area under US military control.

"The Islamic Emirate strongly condemns the bombing targeting civilians at Kabul airport," said a statement released by Mujahid on Twitter.

Zabihullah Mujahid, the Taliban's main spokesman, told AFP that "between 13 and 20" people were killed and 52 wounded in the twin blasts, while Kabul hospitals reported six dead and up to 90 wounded.

The Pentagon said "a number" of US troops died in what spokesman John Kirby called a complex attack.

The "complex attack" near the airport caused a number of US and civilian casualties, Pentagon spokesman John Kirby said in a tweet.

US President Joe Biden had earlier cited an "acute" terrorist threat from the regional chapter of the Islamic State group.

US and allied officials have said they had intelligence that suicide bombers were threatening to attack the airport.

The blasts came as the August 31 deadline loomed for the United States to withdraw its troops, and for Western countries to end their massive airlifts.

According to the city's main Emergency Hospital, at least six people were killed and more than a dozen injured in the blasts.

US President Joe Biden had earlier cited an "acute" terrorist threat from the regional chapter of the Islamic State jihadist group.

An AFP journalist in Kabul saw a plume of smoke rising into the sky from a site near the airport.

"When people heard the explosion there was total panic. The Taliban then started firing in the air to disperse the crowd at the gate," a witness told AFP on condition of anonymity.

"I saw a man rushing with an injured baby in his hands," he added.

The US government and its allies had raised the alarm earlier in the day with a series of advisories warning their citizens to avoid the airport.

No specifics were given in the terror advisories, but Belgium's Prime Minister Alexander De Croo referred to a threat from suicide bombers.

London also issued a warning to its citizens, saying "if you can leave Afghanistan safely by other means, you should do so immediately".

   **- 'Truly heartbreaking' -**

Images posted on social media, which could not be immediately verified, showed men ferrying injured people to safety in wheelbarrows.

In another picture a boy was seen clutching the arm of a man whose clothes were soaked in blood.

More than 95,000 Afghans and foreigners have fled Afghanistan via the US-led airlift since the Taliban movement took control of the country on August 15.

Despite the US and other warnings of a looming terror threat, huge crowds of people desperate to flee the Taliban continued to throng the airport, their bid for a way out becoming increasingly anxious ahead of the August 31 deadline set by Biden to end evacuations and withdraw troops.

Biden and his aides have not budged on the hard deadline -- even as some foreign nations warned they would be forced to leave at-risk Afghans behind.

The Pentagon had earlier Thursday reiterated that operations would continue until the cut-off.

But several Western allies have already wrapped up their airlift operations including Canada, whose government said it was "truly heartbreaking" to leave behind those who wanted to be rescued