An AFP reporter at the scene said the bomb appeared to have struck a military vehicle which had overturned.
The area was sealed off and Afghan officials could not immediately say if any civilians had been struck by the explosion.
Many of the suicide bombings in Afghanistan are carried out by Taliban fighters who were removed from government in a US-led invasion in late 2001 for sheltering al-Qaeda.
There were about 84 suicide attacks to the end of September this year, down from the 119 for the same period last year, according to independent security monitoring group the Afghanistan NGO Safety Office. 

About half were aimed at the international security forces but about three-quarters of the casualties were civilians, it said in a report released last week.