A Taliban suicide attack near the defence ministry in Kabul killed at least 24 people on Monday, including a number of senior security officials, and wounded 91 others, officials said.
Two blasts in quick succession hit a crowded area of the city near government buildings, a market and a main intersection, defence ministry spokesman Mohammad Radmanesh said.
Troops, police and civilians rushing to help victims of the first explosion were caught in the second, triggered when a suicide bomber blew himself up.
"When the first explosion happened people crowded to the site and then the second blast occurred, which was really powerful and killed lots of people," said Samiullah Safi, who witnessed the attack.
The casualty total may increase as more information becomes available, said Mohammad Ismail Kawousi, a spokesman for the public health ministry.
An army general and two senior police commanders were among the dead, a defence ministry official said.
The Taliban claimed responsibility for the attack, which it said killed 58 officers and commanders. The militants have stepped up their campaign against the Western-backed government in recent weeks, following a brief lull after the death of their former leader, Mullah Akhtar Mansour.
The double bombing came less than two weeks after gunmen attacked the American University in Kabul, killing 13 people.
It was the deadliest attack in Kabul since at least 80 people were killed by a suicide bomber who targeted a demonstration on July 23. That assault was claimed by Islamic State.
Government officials have been preparing for a conference in Brussels next month at which foreign donors, concerned about the ability of the Afghan security forces to withstand Taliban violence, are expected to pledge continuing support over coming years.