An Afghan official says a suicide bombing has killed three civilians in eastern Kabul and wounded several others more.
Sunday's blast comes two days before an international conference in Kabul hosting representatives from about 60 nations.
Police official Abdul Ghafor Sayedzada says the bomber was on foot and his target was unclear. Other officials said earlier that the attacker was on a bicycle.
Public health official Kabir Amiri says two hospitals have reported three civilians killed, including a child, plus 23 people wounded.
University student Tamim Ahmad says he saw a man on foot run up to a passing convoy of international troops and detonate an explosives-laden vest. However, Afghan authorities and NATO say no troops were operating in the area.
A security blanket has been thrown over the capital for the conference, with the area that houses the capital's diplomatic and government quarter under virtual lockdown.
At least four loud blasts were heard near the heavily barricaded and fortified area around midnight (1930 GMT) but Kabul is frequently the target of bloody suicide bomb and commando-style attacks.
The Kabul Conference will hear Afghan President Hamid Karzai appeal for a greater say in how billions in development aid is spent as around 150,000 foreign forces tackle an increasingly bloody insurgency.
Donors and other stakeholders are seeking commitments from the government that greater control won't be marked by corruption or incompetence and that Afghanistan is prepared to take on a bigger share of the war.