Seven people have died and 14 were injured as several fuel tankers caught fire on the northern edge of the Afghan capital of Kabul.
Investigators were combing through the dozens of tankers and a petrol station that lay in smouldering ruins, the Interior Ministry said.
There was no immediate indication of whether it was an accident or sabotage.
It came on the same day that the US and Nato officially began the final phase of a withdrawal from Afghanistan, ending a nearly 20-year military engagement.
All 2,500-3,500 American soldiers and about 7,000 Nato allied forces will be out of Afghanistan by September 11, the 20th anniversary of the terrorist attacks in the United States that first brought them into the country.
Interior Ministry spokesman Tariq Arian said the fire began when a spark set a fuel tanker ablaze.
Several tankers nearby were quickly engulfed, sending giant flames and plumes of smoke into the night sky.
The fire in the northern edge of the city engulfed several homes and a nearby petrol station. Several structures were destroyed and electricity to much of Kabul, which usually has only sporadic power, was knocked out.
Lorry drivers blocked the road leading to the area on Sunday, demanding the government provide compensation.
The wounded were being treated mostly for burns in local hospitals.