President Joe Biden says the death of Al Qaeda leader Ayman al-Zawahiri in a US drone strike will bring "One more measure of closure" for the families of terrorist victims.

The Egyptian doctor and surgeon helped coordinate the 9/11 attacks in which four civilian aircraft were hijacked and flown into the World Trade Center's twin towers in New York, the Pentagon near Washington and a Pennsylvania field, killing nearly 3,000 people. 

One US official, speaking on the condition of anonymity, said a drone strike was carried out by the CIA in the Afghan capital Kabul early Sunday morning.

"Now justice has been delivered, and this terrorist leader is no more," Mr Biden said in remarks from the White House. "We never back down."

US intelligence determined with "high confidence" that the man killed was Zawahiri, according to a senior administration official. No other casualties occurred.

First strike since US withdrawal

In his remarks on the successful counter-terrorism operation, Mr Biden said the world would no longer need to fear Zawahiri.

"The United States continues to demonstrate our resolve and our capacity to defend the American people against those who seek to do us harm," he said.

"We make it clear again tonight that, no matter how long it takes, no matter where you hide, if you are a threat to our people, the United States will find you and take you out."

Zawahiri's death in a CIA drone strike raises questions about whether he was being given sanctuary by the Taliban following their takeover of Kabul in August 2021 as the last US-led troops left Afghanistan after 20 years of war.

US officials say that senior members of the Taliban were aware of Zawahiri's presence in Kabul, and maintain that the US had a legal basis for their operation. 

But in a statement, Taliban spokesman Zabihullah Mujahid confirmed that a strike took place and strongly condemned it, calling it a violation of "international principles."

"A house was hit by a rocket in Sherpoor. There were no casualties as the house was empty," Abdul Nafi Takor, spokesman of the interior ministry, said earlier.

One Taliban source, requesting anonymity, said there had been reports of at least one drone flying over Kabul that morning.

The US expects to have continued dialogue with the Taliban. 

With other senior al-Qaeda members, Zawahiri is believed to have plotted the October 2000 attack on the USS Cole naval vessel in Yemen that killed 17 US sailors and injured more than 30 others.

He was indicted in the United States for his role in the August 1998 bombings of the US embassies in Kenya and Tanzania that killed 224 people and wounded more than 5,000 others.

Both bin laden and Zawahiri had eluded capture when US-led forces toppled Afghanistan's Taliban government in late 2001 following the September 11 attacks on the US.

Bin Laden was killed in 2011 by US forces in Pakistan.

Lingering questions about Al Qaeda leader's movements

It was not immediately clear how the United States, which does not have US troops on the ground, confirmed that Zawahiri had been killed. 

A senior official said there were no US personnel on the ground in Kabul when the strike occurred, however, multiple intelligence sources gave "High confidence" that Zawahiri had been killed.

There were rumours of Zawahiri's death several times in recent years, and he was long reported to have been in poor health.

His whereabouts – variously rumoured to be in Pakistan's tribal area or inside Afghanistan – had been unknown until the strike.

A video released in April, in which he praised an Indian Muslim woman for defying a ban on wearing an Islamic head scarf, dispelled rumours that he had died.

Mr Biden's decision to kill Zawahiri is likely to be compared to the cautious stance he initially took in meetings that led to then-president Barack Obama's order for the Pakistan raid that killed bin Laden in 2011.

Then-vice-president Biden acknowledged he advised Mr Obama to take more time, but also told him to "Follow your instincts", ultimately supporting his decision to go ahead.

Sources | ABC / Wires