At least 95 people have been killed and about 163 wounded after a powerful explosion rocked the city centre of the Afghan capital, Kabul.
A plume of smoke was seen rising from the site of the explosion, which happened near the old Interior Ministry building at around 12.15pm local time.
The offices of the European Union and the High Peace Council are also nearby, along with a a number of foreign embassies and the police headquarters.
Saturday is a working day in Afghanistan and witnesses said the area was crowded at the time of the attack.
Nasrat Rahimi, deputy spokesperson for the Interior Ministry, said the attacker was driving an ambulance and told police he was taking a patient to a nearby hospital to get through a security checkpoint. He detonated the explosives at a second check point, Mr Rahimi said.
“It is a massacre,” said Dejan Panic, coordinator in Afghanistan for the Italian aid group Emergency, which runs a nearby trauma hospital. In a message on Twitter, the group said more than 50 wounded had been brought in to that hospital alone.
Buildings hundreds of metres away were shaken by the force of the explosion, which left torn bodies strewn on the street nearby.
People helped the walking-wounded away from the scene as ambulances with sirens wailing inched their way through the traffic-clogged streets of the city centre.
Zabihullah Mujahid, a Taliban spokesman, claimed responsibility for the attack.
Afghan forces have struggled to combat the Taliban since the US and Nato formally ended their combat mission at the end of 2014. Last week, Taliban militants killed 22 people in a luxury Kabul hotel.
In December, an attack on a Shiite cultural centre in Kabul killed at least 41 people in an attack claimed by the Isis.
Afghan authorities have also had to contend with a growing Isis affiliate that has carried out a number of large-scale attacks in recent years.
The latest attack will add pressure on President Ashraf Ghani and his US allies, who have expressed growing confidence that a new more aggressive military strategy has succeeded in driving Taliban insurgents back from major provincial centres.
The United States has stepped up its assistance to Afghan security forces with the aim of breaking a stalemate and forcing the insurgents to the negotiating table.
But the Taliban have dismissed suggestions that they have been weakened by the new strategy and the latest attacks have demonstrated that their capacity to mount deadly, high-profile attacks remains undiminished.