Militants launched a gun and bomb attack on the interior ministry in Kabul Wednesday, days after the Taliban vowed to target military and intelligence centres in the Afghan capital.
Special forces were on the scene, a security source told AFP, after an explosion at a checkpoint leading to the compound. The source said at least four attackers then began firing.
No group immediately claimed responsibility for the attack, which began at around 12.30pm and which witnesses said was continuing.
"We can confirm an explosion and gunfire at the first checkpoint of the interior ministry building. Security forces are there to assess the situation," interior ministry spokesman Najib Danish told AFP, in a statement echoed by police.
He said the first explosion was "probably a suicide bomber". A security source said there had been more explosions afterwards but could not confirm how many.
"The attackers have not been able to enter the main building," Danish said, adding that gunfire could still be heard at the checkpoint.
He said at least one police officer was confirmed wounded so far.
Both the Taliban and the Islamic State group have stepped up their attacks on Kabul, making the capital the deadliest place in the country for civilians in recent months.
Last week the Taliban called on Kabul residents to "keep away" from military and intelligence centres in the heavily fortified city, saying they plan more assaults as part of their annual spring offensive.
"Therefore, to avoid civilian casualties and only cause damage to enemy military, we are asking Kabul residents to keep away... we don't want even a single innocent civilian to be killed," said a statement published online.
In response, the defence ministry said police and troops are "ready to protect the people with all means possible", and would not allow the militants to reach their "un-Islamic and inhuman goals".
The Taliban did not define what was meant by "military and intelligence centres".
Such targets are difficult to avoid given that the overcrowded city is the heart of the country's intelligence, government and military operations and plagued by traffic jams due to ubiquitous checkpoints and barriers.
Kabul accounted for 16 percent of all civilian casualties last year, when 1,831 civilians were killed or wounded nationwide, according to the United Nations Assistance Mission in Afghanistan.
The UN has warned that 2018 could be even deadlier.
A checkpoint in Kabul: the Taliban have vowed to target the city despite tight security