A Taliban suicide bomber blew himself after joining a queue to enter a police office in Kabul on Monday, killing 20 people and wounding at least 29 in the worst such attack this year.
The Afghan capital was hit by a series of suicide attacks last month as the Taliban stepped up their campaign against the Western-backed government. They coincided with renewed efforts to revive a peace process with the Islamist insurgent movement that stalled last year.
The Interior Ministry released a statement with the number of casualties.
In a separate statement, the NATO mission condemned the attack, which it said killed 20 police officers and wounded 25 others as well as seven Afghan civilians.
"Once again, terrorists have targeted a populated area with no regard for innocent lives," said Brig. Gen. Wilson Shoffner, Resolute Support deputy chief of staff for communications.
The Taliban claimed responsibility for the attack in a statement that said 40 police officers had been killed or wounded. The group often makes exaggerated casualty claims for its attacks.
Ambulances and police vehicles rushed to the explosion site in the crowded Dehmazang district west of the city, near the Kabul traffic directorate, which is visited by those seeking driving licences and other documents.
"I saw three bodies on the ground and a number of other people wounded, then ambulances arrived and took all the victims away," witness Mohammad Ajmal said.
Last August, a Taliban suicide bomber killed dozens of students at a police academy in Kabul, using a similar tactic by joining a queue waiting to enter the compound.
The Afghan National Civil Order Police (ANCOP) was set up as a gendarmerie-style unit to control riots and urban disorder but have also been used in counterinsurgency roles against the Taliban.