A passenger bus in southwestern Iran overturned on Friday evening, killing 26 female high school students on board, Iranian media reported on Saturday.

Eighteen others were injured when the bus, carrying students from the town of Borujen, flipped on the Izeh-Lordegan road, about 700 km southwest of the capital Tehran, Iranian media reported.

"Travelling at excess speeds on slippery roads was the cause of this accident," Colonel Samad Esfandiari, a highway patrol official, told the Iranian Students' News Agency.

The injured were taken to various hospitals in southwest Iran for treatment, state television said.

Road traffic accidents kill nearly 28,000 people and injure or disable 300,000 people a year in Iran, a country of 75 million people, according to statistics from Unicef, the United Nations Children's Fund.

Road accidents occur at a rate 20 times higher than the world average in Iran, Unicef said. -Reuters