Six people were killed when a cargo helicopter crashed in northern Iran early on Friday, state-run television reported.
The pilots lost control of the helicopter, killing three of the passengers when they fell out of the aircraft while it was still flying, the report said.
The two pilots and another passenger died when the helicopter burst into flames after it crashed in the Larijan region, about 85 kms north of Tehran.
The state television report said the pilots lost control because the helicopter was overloaded.
It was carrying iron bars to workers who were building a shelter for mountain climbers, the report said.
Iran has a history of aircraft accidents. In January, a military flight carrying a commander of the country's elite Revolutionary Guards and 10 others crashed, killing everyone on board.
A month earlier, a military transport plane crashed into a building near Tehran's airport, killing 115 people.
Critics have said the planes and helicopters are poorly maintained. The government has blamed the US trade embargo, which makes it impossible for Iran to buy parts for its American-built aircrafts.