A suicide bomber blew himself up outside a gate of the Afghan Defence Ministry in Kabul on Saturday and the attack was followed by small-arms fire, said a spokesman for Afghanistan's NATO-led force.
There was no immediate word on casualties in the blast which took place during a visit by U.S. Defense Secretary Chuck Hagel.
The International Security Assistance Force (ISAF) spokesman said Hagel was nowhere near the explosion. A U.S. defence official said Hagel was in a safe location at an ISAF facility.
The attack underscored the security challenges facing Afghanistan as U.S.-led NATO forces prepare to leave the country by the end of 2014.