The death toll from a Taliban attack on a government security agency's building in the Afghan capital on Tuesday has risen to at least 28, the Kabul police chief said, with more than 320 wounded.
Police chief Abdul Rahman Rahimi said civilians and members of the Afghan security forces were among the dead and wounded.
The Taliban claimed responsibility for the attack. It was the first in the Afghan capital since the Islamist militant group declared the start of their spring offensive a week ago.
President Ashraf Ghani condemned the attack "in the strongest possible terms" in a statement from the presidential palace, only a few hundred metres away from the scene of the blast.
Fighting has raged around the symbolically important northern city of Kunduz in the week since the Taliban announced their annual spring offensive, although the capital has been relatively quiet since the April 12 announcement.
Kunduz, Afghanistan's fifth-largest city, fell briefly to the Taliban last September in the biggest blow to Ghani's government since NATO-led forces ended their combat operations at the end of 2014.
Gunfire rang out for more than 30 minutes after the blast, according to Reuters witnesses at the scene. Pictures showed windows blown out at the front of an office that houses a National Directorate of Security (NDS) unit
The Taliban said on their Pashto-language website that they had carried out the suicide bombing on "Department 10", an NDS unit, which is responsible for protecting government ministers and VIPs.
They said a suicide car bomber blew up the main gate at the front of the office, allowing other fighters, including more suicide bombers, to enter the heavily guarded compound.
A separate statement by Taliban spokesman Zabihullah Mujahid said attackers were engaged in a gunbattle with Afghan securityforces inside the building.
It was not immediately possible to verify the details of the Taliban's claim with government officials. The Islamist group often exaggerates details of attacks against government and military targets.
The Taliban-led insurgency has gained strength since the withdrawal of most international combat troops, and the Taliban are stronger than at any point since they were driven from power by U.S.-backed forces in 2001.
A thick plume of black smoke had been seen rising from the area near the sprawling U.S. embassy complex in the centre of Kabul immediately after the blast.
Warning sirens blared out for some minutes from the embassy compound, which is also close to the headquarters of the NATO-led Resolute Support mission.
The U.S. embassy and the NATO mission both said they were not affected by the blast.