Who are Isis-K, and what is their relationship with the Taliban?
Coordinated suicide bomb blasts at Kabul airport on Thursday have left at least 170 dead and many more injured.
Isis-K has claimed responsibility for the attack, which targeted US troops and Afghans attempting to secure the last remaining places on military evacuation flights out of the country.
On Friday, the US said it killed a "planner" for the group in an air strike in Afghanistan.
The threat of further attacks around Kabul Airport will increase as Western troops get closer to leaving the country, Defence Secretary Ben Wallace said on Friday, with Isis-K hoping to show it drove foreign troops from Afghanistan.
"The threat is obviously going to grow the closer we get to leaving," he told Sky News. "The narrative is always going to be, as we leave, certain groups such as ISIS will want to stake a claim that they have driven out the US or the UK."
On Thursday night, President Joe Biden pledged to "hunt down" the attackers and ordered his military to plan strikes.
He said: "Know this: we will not forgive, we will not forget. We will hunt you down and make you pay."
Here we look at how Isis-K came to exist and why it poses such a threat to US forces in Afghanistan.
Who are Isis-K?
As the name suggests, Isis-K is an offshoot of the Islamic State terrorist group that once held huge swathes of territory in northern Syria and Iraq.
Since 2014, the splinter group has been mostly based in eastern Afghanistan, part of an area known as the Khorasan province - hence the acronym Isis-K.
According to a US security think-tank, the Centre for Strategic and International Studies [CSIS], Isis-K launched a hundred attacks on civilians in Afghanistan and Pakistan between 2015 and 2017.
It was also responsible for around 250 attacks on US, Pakistani and Afghan forces during that same time period, and since then the number is likely to have risen further.
More recently, a United Nations report estimated that the group has “between 500 and 1,200 fighters”, though some experts say that figure could rise to 10,000 in the coming years.
The group is said to be trying to swell its ranks in Kabul, the scene of desperate evacuation efforts by Western allies.
The founding leader of Isis-K, Hafiz Saeed Khan, was killed by US forces in 2016 and has since been replaced by Iraqi citizen Shahab Muhajir, according to analysis by CSIS and BBC Urdu.
What is its relationship with the Taliban?
It is not a friendly one. The Taliban and Isis-K are regional foes due to differing ideologies and bitter competition for territory in the Khorasan area and beyond.
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.
Earlier this year, the Taliban claimed to have wiped out the entire Isis-K presence in the northern province of Jowzjan. It has also seized northwestern territory held by Isis-K in recent weeks.
And in Jalalabad, a city in eastern Afghanistan, hundreds of Isis-K fighters have surrendered to the Taliban.
A recent editorial in an IS newsletter claimed that the Taliban takeover of Afghanistan was a US-backed conspiracy and poured scorn on their credentials as true jihadists, reflecting deep animosity towards the insurgents.
Why is the West concerned about Isis-K?
Jake Sullivan, Mr Biden’s national security adviser, said previously that the risk of Isis-K carrying out an attack on Kabul airport was “real, acute” and “persistent”.
“It is something that we are focused on with every tool in our arsenal,” Mr Sullivan told CNN.
He did not provide further details on what sort of attack Isis-K might be planning, but US officials told the New York Times it could take the form of a missile launch on an evacuating plane.
Are there concerns about Isis-K attacks in Britain and Europe?
There are concerns that people who pose a “direct threat” to UK security are trying to slip through checkpoints at Kabul airport and board evacuation flights.
Six individuals on Britain’s “no fly list” have been flagged during security checks at the airport, and one of them managed to reach Birmingham airport, MPs were briefed this week.
The Home Office says that, after further checks on the individual who reached the UK, he is no longer considered a “person of interest” to security services.
It is unclear if any of the people flagged as a security threat have links to Isis-K.
SOURCE: The Telegraph