The explosion happened at the rural rehabilitation and development ministry around 4:30 pm, police spokesman Hashmat Stanikzai told AFP.
Ministry spokesman Fraidoon Azhand said the bomber struck at a security gate as employees were exiting the compound to go home.
It is the second time in just over a month that the ministry has been targeted by militants.
The Islamic State group claimed responsibility for that attack.
Today's blast comes as a UN report shows a record number of civilians were killed in the first six months of 2018, with militant attacks and suicide bombs the leading causes of death.
The toll of 1,692 fatalities was one per cent more than a year earlier and the highest for the period since the United Nations Assistance Mission in Afghanistan (UNAMA) began keeping records in 2009.
Another 3,430 people were wounded in the war, down five per cent from the same period last year, the report said.
The record high death toll came despite an unprecedented ceasefire by Afghan security forces and the Taliban last month that was largely respected by both sides, UNAMA said.
The ceasefire for the first three days of Eid was marked by scenes of jubilation as security forces and Taliban fighters celebrated the Islamic holiday, raising hopes that peace was possible after nearly 17 years of conflict.
Suicide bombs and "complex" attacks that involve several militants accounted for 1,413 casualties -- 427 deaths and 986 injuries -- up 22 per cent from a year earlier.
UNAMA attributed 52 per cent of those casualties to IS, mainly in Kabul and Nangarhar where the group established a stronghold after emerging in Afghanistan in 2014.
The Taliban was responsible for 40 per cent.
While the Taliban is Afghanistan's largest militant group and holds or contests more territory than any other, IS has repeatedly demonstrated its ability to carry out devastating attacks in urban areas.
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)