Seventeen people died when a bus crashed into an oncoming truck and caught fire in southweatern Iran, Mehr news agency reported on Friday quoting an official.
The accident occurred on Thursday near Haftekl city in the southwestern province of Khuzestan, Alireza Najafi, a local official, was quoted as saying.
"Thirteen people were killed upon impact," said Najafi, adding four more people died of later in hospital from serious burns injuries.
An investigation was launched into the cause of the crash.
Iran is one of the world's deadliest countries for road accidents. About 20,000 people are killed each year in a nation with a little over 17 million vehicles for its 77-million-strong population.
Despite the high number of crashes, the authorities say deadly accidents have decreased in recent years as police take a tougher line on road rules.
In early April a pickup truck smuggling fuel crashed into a car carrying 15 illegal Afghans in southeastern Iran, bursting into flames and killing all on board as well as three Iranians.