A major Taliban suicide bomb and gun attack on a government security office in central Kabul during rush hour has killed at least 28 people and wounded more than 320.
President Ashraf Ghani condemned Tuesday's assault "in the strongest possible terms" in a statement from the presidential palace, only a few hundred metres away from the scene of the blast in the Afghan capital.
The insurgency led by the Afghan Taliban has gained strength since the withdrawal of most international combat troops at the end of 2014, and the Islamist group is believed to be stronger than at any point since it was driven from power by US-backed local forces in 2001.
Police chief Abdul Rahman Rahimi said civilians and members of the Afghan security forces were among the dead and wounded.
The brazen attack began with a suicide car bomb and security forces and militants then exchanged gunfire, Reuters witnesses near the scene said.
The Taliban said on their Pashto-language website that they had carried out the suicide bombing on "Department 10", an NDS (National Directorate of Security) 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.
Taliban spokesman Zabihullah Mujahid said in a separate statement that the 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.
A thick plume of black smoke was seen rising from the area near the sprawling US embassy complex 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.
A man stands inside his damaged shop near the scene of a bomb blast that targeted the Ministry of Defense in Kabul, Afghanistan, 19 April 2016. Source: AAP
The US embassy and the NATO mission both said they were not affected by the blast.
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.
Tuesday's blast came days after a United Nations report said urban warfare had caused a spike in the number of deaths and injuries among women and children in Afghanistan this year as the Taliban intensify their campaign against Ghani's Western-backed government.
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