At least 90 Afghan civilians and 12 members of the US military have been killed in twin suicide bombings at Kabul's international airport as foreign evacuation efforts continue.

The attack comes just a day after Western nations - including New Zealand - advised citizens and visa holders on the ground to avoid Hamid Karzai International Airport due to terrorism threats. The site has become the centre point of tensions in Afghanistan, with thousands of people flocking to it with hopes of getting on an evacuation aircraft out of the country, which recently fell to the Taliban.

US intelligence prior to the attacks suggested the main threat came from a group called ISIS-K. 

"The longer we stay, starting with the acute and growing risk of an attack by a terrorist group known as ISIS-K, an ISIS affiliate in Afghanistan - which is the sworn enemy of the Taliban as well - every day we're on the ground is another day we know that ISIS-K is seeking to target the airport and attack both US and Allied forces and innocent civilians," President Joe Biden said earlier this week. 

That appears to have borne out, with Islamic State on Friday morning claiming responsibility for the bombings.

Who is ISIS-K?

ISIS-K, also known as Islamic State-Khorasan Province, is an affiliate of Islamic State active in Afghanistan and Pakistan. The group gets its moniker from Khorasan, a historical region covering what is now Afghanistan and other parts of central Asia.

It was formed in 2015 after six members of the Tehrik-i-Taliban Pakistan Islamic militant group broke away and pledged allegiance to then-Islamic State leader Abu Bakr al-Baghdadi. Its focus is to control the Khorasan region and set it up to be part of Islamic State's caliphate. 

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A number of other militants from Afghanistan and Pakistan have since joined the group as well as defectors from the Taliban. ISIS-K opposes the Taliban as it doesn't believe it is devout enough to its Islamic cause and for negotiating with the United States. It's been suggested ISIS-K may look to cause disruption in Kabul to undermine the Taliban's rule.

"Spectacular attacks in Afghanistan and attempts to conduct such attacks in the West are highly likely in coming weeks and months," Jennifer Cafarella, a national security fellow at the US Institute for the Study of War told Business Insider. "ISIS will attempt to erode the Taliban's governance and attack the Taliban's religious legitimacy on the ground."

ISIS-K has been described as the most violent of the Islamic State affiliates. Among the terrorist attacks it has claimed responsibility for is a suicide bombing at a political rally in Mastung, Pakistan in July 2018 which killed 149 people and a bombing at a funeral in Afghanistan's Nangarhar province which killed 32. 

It also has history in Kabul, including attacks at a wedding, a Sikh temple, a government ministry building and a voter registration centre. It's thought to be behind an attack on a maternity hospital in the Afghan capital last May that killed 24, including newborn babies and mothers. 

Speaking to The AM Show on Friday, Charlotte Bellis of Al Jazeera said the US and Taliban have a "mutual hatred" of the group.

"Their [modus operadi] has basically been to target civilian populations, minorities, especially in Kabul, schools, girls' schools. Just no rhyme or reason to their targets. If they can kill as many innocent people as possible, they will," she said.

"That is why I think the airport was in their crosshairs, as they thought there is a lot of desperate people here who are innocent and we can do a lot of damage, and they targeted it.

"It is very hard to understand why they would ever do something like this other than they are just trying to inflict the most casualties they can."

As Islamic State collapsed in recent years in the face of the US Coalition, ISIS-K also fell from its zenith. However, a UN report from June says it still had up to 2200 fighters, including in the province of Nangarhar, which is both close to Kabul and the Pakistan border, allowing for drug smuggling.

"ISIL-K is seeking to remain relevant and to rebuild its ranks, with a focus on recruitment and training of new supporters potentially drawn from the ranks of Taliban who reject the peace process," the report says. 

With the fall of Kabul, there have been major concerns that extremist groups in Afghanistan could take advantage of the chaos.