The Taliban have claimed responsibility for a huge explosion in the Afghan capital Kabul on Tuesday morning.
Several people have died and more than 200 wounded after a suicide attacker detonated a car bomb. Gunfire was ongoing between security forces and the militants at midday Kabul time (0830 BST), according to Reuters witnesses at the scene.
The militant group launched the attack in the height of the morning rush hour. It comes a week after it said it was launching a "spring offensive" and warned of "large-scale attacks". The explosion targeted the office of Afghanistan's main security agency.
President Ashraf Ghani condemned the attack "in the strongest possible terms" in a statement from the presidential palace, only a few hundred meters away from the scene of the blast in central Kabul.
"Such cowardly terrorist attacks will not weaken the will and determination of Afghan security forces to fight against terrorism," said the President.
Pictures showed windows blown out at the front of an office that houses a National Directorate of Security (NDS) unit.
The Health Ministry said civilians and members of the Afghan security forces were among those caught in the attack, and several people had been killed and more than 200 wounded.
Those casualty numbers were expected to rise, said ministry spokesman Ismail Kawosi.
The Taliban announced the beginning of their spring offensive on April 12, and fighting has raged around the symbolically important northern city of Kunduz since then, although the capital had been relatively quiet.
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.
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. These reports are as yet uncomfirmed.
Taliban spokesman Zabihullah Mujahid said in a separate statement that the attackers were engaged in a gun battle with Afghan security forces 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 believed to be stronger than at any point since they were driven from power by US-backed forces in 2001.
Additional reporting from Reuters.