A Taliban suicide car bomber attacked an office of Afghanistan's main national security agency in Kabul on Tuesday, killing or wounding several people, the first assault in the capital since the group declared their new spring offensive a week ago. According to a aljazeera report, at least 22 people were killed and 200 wounded after a suicide bomber blew himself up near the defence ministry in the heart of the city. 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. Several people were killed and wounded in the blast, which struck at the height of the morning peak hour, the palace said. 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 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 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.