A suicide bombing has killed at least 95 people and injured 158 others in the centre of Afghanistan's capital, Kabul, officials say.
Attackers drove an ambulance laden with explosives past a police checkpoint in a secure zone, home to government offices and foreign embassies.
The Taliban have said they carried out the attack, the deadliest for months.
US President Donald Trump called for "decisive action" against the group after the "despicable" bombing.
A week ago, Taliban militants killed 22 people in a luxury Kabul hotel.
What happened in the latest attack?
Witnesses say the area - also home to offices of the European Union, a hospital and a shopping zone known as Chicken Street - was crowded with people when the bomb exploded on Saturday at about 12:15 local time (08:45 GMT).
Nasrat Rahimi, deputy spokesperson for the Interior Ministry, said the attacker got through a security checkpoint after telling police he was taking a patient to nearby Jamhuriat hospital.
He detonated the bomb at a second checkpoint, said Mr Rahimi.
The BBC's Zia Shahreyar, speaking from the scene, says it is not easy to get through the checkpoints. Cars are searched and drivers' identities checked.
He adds that questions will be asked about how the attacker got through.
The International Committee of the Red Cross said the use of an ambulance was "harrowing".
What did witnesses say?
MP Mirwais Yasini told the BBC the area looked like a butcher's shop afterwards.
He was having lunch at his family home, just metres away, when the blast went off. "First of all we thought it was inside our house," he said. Then he went outside and saw scattered bodies. "It is very, very inhumane."
Another witness, a software engineer who wished to remain anonymous, told the BBC he was about a kilometre (two thirds of a mile) away when he heard the noise.
"I saw a huge flame," he said. "The smoke was pungent. It entered my eyes and I was not able to see for some time."
He said when he moved closer he saw the dead bodies, and it looked like a "brutal graveyard".
"It was a terrible moment. [The area] is completely destroyed."
What was the response?
The Afghan government has condemned the bombing as a crime against humanity, and accused Pakistan of providing support to the attackers.
The Taliban control large swathes of Afghanistan and parts of neighbouring Pakistan.
Pakistan denies supporting militants that carry out attacks in Afghanistan. This month, the US cut its security aid to Pakistan, saying it had failed to take action against terrorist networks on its soil.
What is the reaction in the rest of the world?
In a statement, US President Donald Trump said:
"I condemn the despicable car bombing attack in Kabul today that has left scores of innocent civilians dead and hundreds injured. This murderous attack renews our resolve and that of our Afghan partners."
UN Secretary General Antonio Guterres said: "Indiscriminate attacks against civilians are a serious violation of human rights and humanitarian laws, and can never be justified."
In France, the Eiffel Tower turned off its lights at midnight on Saturday as a mark of respect for the dead and injured.
Paris Mayor Anne Hidalgo wrote on Twitter: "The city of Paris and Parisians are with the Afghan people who are once again facing terrorist barbarity," she said.
How does it compare to other recent attacks?
The attack is the deadliest in Kabul in several months.
In October, 176 people were killed in bomb attacks across Afghanistan in one week. The country's security forces in particular have suffered heavy casualties at the hands of the Taliban, who want to re-impose their strict version of Islamic law in the country.
In May, 150 people were killed by a suicide bomb attack in Kabul. The Taliban denied any role, but the Afghan government says its affiliate, the Haqqani group, carried it out with support from Pakistan.
Who are the Taliban?
- The hardline Islamic Taliban movement swept to power in Afghanistan in 1996 after the civil war which followed the Soviet-Afghan war, and were ousted by the US-led invasion five years later, but returned to run some key areas
- In power, they imposed a brutal version of Sharia law, such as public executions and amputations, and banned women from public life
- Men had to grow beards and women to wear the all-covering burka; television, music and cinema were banned
- They sheltered al-Qaeda leaders before and after being ousted - since then they have fought a bloody insurgency which continues today
- In 2016, Afghan civilian casualties hit a new high - a rise attributed by the UN largely to the Taliban
- Civilian casualties remained at high levels in 2017, the UN said