People in Afghanistan have been urgently warned to stay away from Kabul airport, due to an "incredibly imminent and lethal" threat of terrorist attacks. While evacuees from the UK and other western nations may have received the message, tens of thousands of Afghans have not, with people swarming the airport in the desperate hope of fleeing the Taliban's tightening grip.

       On Tuesday, US President Joe Biden warned of a potential terror attack by ISIS-K.

       He said: "Every day we’re on the ground is another day that we know ISIS-K is seeking to target the airport and attack both US and allied forces and innocent civilians."

       But is ISIS-K the same as ISIS? Or a new group altogether?

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       ISIS-K is an offshoot of ISIS - often referred to as Islamic State or Daesh.

       The 'K' stands for Khorasan - a region in Afghanistan where the splinter group is based.

       A recent United Nations report estimated ISIS-K had "between 500 and 1,200 fighters", and is expected to grow.

       The group is said to be responsible for some of the worst atrocities in Afghanistan in recent years.

       One attack at a maternity hospital in Kabul last year killed 24 people including mothers and newborns.

       Approximately 100 attacks on Afghan civilians took place between 2015 and 2017 at the hands of ISIS-K, as well as more than 250 on US, Pakistani and Afghan forces in the same period.

       The group is led by an Iraqi militant called Shahab al-Muhajir. Previous leaders have been killed or captured by US and Afghan forces.

       Worryingly, ISIS-K are believed to have a fractious and hostile relationship with the Taliban, the group which has taken control of Afghanistan and considered by many world powers to be a terrorist organisation itself.

       The two groups differ on ideologies and are locked in fierce competition for territory.

       ISIS as a whole is anti-Taliban, having opposed how Taliban leaders negotiated with the US in their return to power.

       A recent editorial in an ISIS newsletter claimed that the Taliban takeover of Afghanistan was a US-backed conspiracy and denied the group was true jihadists.

       US intelligence officials believe that some of ISIS-K’s recruits are Taliban defectors, while there have been unconfirmed reports of the Taliban executing at least one senior ISIS-K figure since taking over Afghanistan.

       If ISIS-K were to attack Kabul airport, it would have the double effect of harming western forces, while at the same time undermining the authority of Afghanistan's incoming Taliban rulers.

       Jake Sullivan, Joe Biden’s national security adviser, said the threat of an ISIS-K attack is “real, acute" and "persistent”.

       He said: "It is something that we are focused on with every tool in our arsenal."

       And UK Armed Forces Minister James Heappey told BBC News on Thursday morning the intelligence was "incredibly imminent and lethal".

       "We are not just being overly cautious," he said.