At least 90 people are reported to have died and scores more have been hurt in a blaze which began when a fuel tanker crashed into buses in south-east Iran.
The crash happened on a busy road near the Pakistani border
The petrol tanker hit vehicles which had stopped at a police post outside the city of Zahedan on the road from Bam, a local official told state TV.
A Red Crescent official said 90 bodies had been recovered, some of which are said to be burnt beyond recognition.
An inquiry has begun into the crash on the main road from Iran to Pakistan.
The tanker had been travelling into Zahedan, about 1,100km (690 miles) from Tehran.
It struck the buses near Nosrabad, about 110km west of the city, as they were undergoing routine checks at the police post.
Police posts are common in the region which is a favoured route for drug smugglers.
Reports of the accident began to emerge on Friday morning though it happened at 2215 local time (1745 GMT) on Thursday.
There have been varied estimates of the number of dead and injured, but the BBC's Jim Muir in Tehran says the accident is one of the worst single losses of life on Iran's roads.
Zahedan Governor Heidar Ali Nouraei told state TV: "The disaster is so grave we cannot identify faces and cannot differentiate between corpses."
Many of the passengers burned to death because of a lack of fire-fighting equipment at the scene, he added.
Policemen at the post said the tanker, which was carrying 18,000 litres (4,680 gallons) of petrol, had been going too fast and careered out of control before turning over.
It hit one of the buses and burst into flames as leaking petrol turned the whole area into an inferno, incinerating the buses and several other vehicles.
Reports suggest that at least one other lorry - possibly a second tanker or a vehicle carrying tar - was caught up in the blaze, which firemen took more than two hours to extinguish.
Around 22,000 people are killed every year in traffic accidents across Iran.
On a monthly average, that is higher than the death rate in the eight-year war with Iraq in the 1980s, our correspondent notes.
In February, about 300 people were killed when a train carrying fuel and chemicals caught fire and exploded in the north-east of the country.