Nato's International Security Assistance Force could not immediately confirm the blast.
Foreign soldiers and their Afghan counterparts sealed off the area, the reporter said.
The explosion was near a Nato-run military outpost that used to be the home of Taliban leader Mullah Mohammad Omar, whose movement is blamed for a wave of attacks in Afghanistan.
Also on Tuesday, at least nine policemen were killed in a battle with Taliban-linked fighter and bomb attacks in the southern Afghanistan province of Kandahar, a police commander said.
Five policemen were killed in an gunfight with Taliban-linked fighters who attacked their remote outpost in Shorabad, a district on the Afghan-Pakistani border, Sayed Agha Saqeb said.
Four other officers, who were despatched to the scene of the fighting as reinforcements, were killed when their vehicles were blown up by remote-controlled bombs, he said.