The US has killed the leader of al-Qaeda, Ayman al-Zawahiri, in a drone strike in Afghanistan, President Joe Biden has confirmed.

He was killed in a counter-terrorism operation carried out by the CIA in the Afghan capital Kabul on Sunday. He and Osama Bin Laden plotted the 9/11 attacks together, and he was one of America's most wanted terrorists. Mr Biden said al-Zawahiri had "carved a trail of murder and violence against American citizens".

"From hiding, he co-ordinated al-Qaeda's branches and all around the world, including setting priorities for providing operational guidance and calling for and inspired attacks against US targets," the president said in a live television address from the White House. "Now justice has been delivered and this terrorist leader is no more," he added.

The FBI updated its Most Wanted Terrorist poster on Monday with Zawahiri's status: "Deceased." The 71-year-old Egyptian doctor took over al-Qaeda after the death of Bin Laden in 2011. Mr Biden said he had given the final approval for the "precision strike" after months of planning.

So-called Islamic State, the Taliban, and al-Qaeda are all radical jihadist groups, but they are not all the same.

The so-called Islamic State, al-Qaeda and now the Taliban are radical jihadist groups focused on ridding the world from the threat, as they perceive it, that Western culture poses to Islam.

However, although broadly speaking they share a similar ideology, their views actually differ significantly – so much so that the three groups have often found themselves in conflict with one another.  

And although there's no disputing the fact that IS have dominated the media in recent months, both al-Qaeda and the Taliban are still very much at large.

But what are the differences between these three prominent terrorist organisations? 

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.