Sporadic loud blasts were heard in the Afghan capital ahead of a major conference on the country's future.
Many foreign ministers, including US Secretary of State Hillary Clinton, are in Kabul for Tuesday's meeting.
A security blanket has been thrown over the city for the conference, with the area housing the capital's diplomatic and government quarter under virtual lockdown.
At least four loud blasts were heard near the heavily barricaded and fortified area at around midnight local time.
Afghan security officials were not available to comment.
A spokesman for the NATO-led International Security Assistance Force said that while they had heard the blasts, they had no information about them.
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 will not be marked by corruption or incompetence and that Afghanistan is prepared to take on a bigger share of the war.
Kabul is frequently the target of bloody suicide bomb and commando-style attacks.
