A pickup truck smuggling fuel crashed on Friday into a car carrying 15 Afghans in southeastern Iran, bursting into flames and killing all on board as well as three Iranians, media reported.
"The crash and resulting fire claimed the lives of 15 Afghans who had entered the country illegally," the state IRNA news agency quoted local official Sadeq Dadollahpour as saying.
He attributed the accident to the "excessive speed" of both vehicles.
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The Mehr news agency said the crash took place in Kerman province on a transit route for Afghans illegally crossing the border in the hope of finding work in the Islamic republic.
Nearly a million Afghans live in Iran illegally, according to official figures released in 2012.
Iran is one of the world's deadliest countries for road accidents. Around 20,000 people are killed each year in a nation with a little over 17 million vehicles for its 75-million-strong population.
Despite the high number of crashes, the authorities say deadly accidents have decreased in recent years as police take a more rigid line on the rules of the road.