Kabul airport bombing: What is Islamic State Khorasan or ISIS-K?

The Islamic State (IS) has claimed responsibility for two bomb attacks in Kabul that has left dozens of US and Afghans dead. IS has no friends in the Taliban, and there were reports of a running battle between the Taliban and IS in the streets of Kabul.

While it is a developing situation, the attack puts the NATO evacuation in jeopardy and some nations have already stated their intention to abandon the mission.

What has happened in Kabul?

Two powerful explosions rocked the Afghan capital this evening; one at the gates of the airport and another in the center of the city.

At least 60 people have been killed and 140 others wounded, a senior health official in Kabul told the BBC. 12 US troops have been killed so far, making it the army's deadliest day in Afghanistan since 2011.

At the airport, a suicide bomber detonated at Abbey Gate where Afghans are desperately queuing for escape. The explosion was followed by an assault by gunmen.

In the center, the attack was outside the Baron hotel, which has been used to process Afghans who are fleeing to the west. The attackers fought with Taliban who had been stationed outside the hotel, according to reports.

NATO had been warning of a "very credible" terrorist threat and the British government urged its nationals to stay away from the airport as the evacuation enters its final stages.

More of our coverage on the unfolding situation in Kabul:

What is Islamic State doing in Afghanistan?

The prime suspects are an offshoot of the Islamic State of Iraq and Syria, known as the Khorasan province (ISKP). The group was started when ISIS had captured large swathes of Iraq and Syria in 2014.

The airport provides a perfect target venue for the kind of attack that IS relishes. Charlie Winter, a senior research fellow at London University’s International Centre for the Study of Radicalisation (ICSR), said the situation was also a “perfect meeting of diverse targets” in Afghanistan: the US military, Afghans who have helped the western effort and the Taliban, which the ISKP see as “apostates”.

The Taliban and ISKP have been involved in skirmishes over the years to wrestle control from one another. The Taliban are much stronger in Afghanistan but the ISKP could have an advantage with multiple revenue streams coming in from sister-groups around the world. An attack in Kabul signals that the ISKP is not yet defeated, even if the Taliban control Afghanistan.

The large, sprawling mountains of Afghanistan provide as good a haven for the ISKP as the Taliban have had for the last two decades.

The Taliban has "strongly" condemned the attack, which it said took place in an area where US forces are responsible for security. The attacks are an embarrassment for the group as it seeks to prove on the world stage that it can safely govern a country.

What does the bombing mean for the evacuation?

The NATO reaction has been mixed. The UK government was quick to announce that their mission would continue, but other nations have decided the threats are too much.

British PM Boris Johnson called the attacks "barbaric" and "despicable."

Before the attack, a number of countries including Germany, the Netherlands and Canada, had announced that they could no longer conduct flights, citing safety concerns. Turkey has announced that its troops, who had been providing security at the airport for six years, were withdrawing.

The US remains committed to its August 31 deadline.