State TV said the plane's tail struck the cables of an electricity tower before it hit the ground and burst into flames. The official IRNA news agency said the plane suffered an engine failure. Whatever the ultimate cause, quick thinking by the pilot may have saved some lives.
"We should be thankful to God that the pilot did all he could to steer the plane away from residential buildings and fortunately did not crash into them. Otherwise, we would have been dealing with a much worse crisis," said Jalal Maleki, spokesman of Tehran's Fire Department.
Known as an IrAn-140 or Iran-140, the twin-engine turboprop is a version of the Antonov An-140 regional plane and is assembled under license in Iran. It can carry up to 52 passengers.
A Ukranian-made An-140 crashed near the central Iranian city of Isfahan in 2002, killing 46 mostly Ukranian and Russian experts traveling to witness the maiden flight of the Iranian-built version of the plane.
A similar Iranian-made version crashed during a training flight in Isfahan in February 2009, killing five onboard, according to a report by state-run Press TV at the time.
Iranian airlines, including those run by the state, are chronically strapped for cash, rely on aging planes and have a spotty maintenance record.
While some operate Boeing and Airbus models, spare parts for Western-made planes are often hard to come by — largely because of sanctions aimed at Iran's nuclear program.
Those difficulties have left Iranian airlines increasingly reliant on planes developed by the Soviet Union and its successor states, though parts for aging Soviet-era planes can also be tough to get.
At the crash site, members of the elite Revolutionary Guard worked to secure the scene from onlookers while security and rescue personnel combed the wreckage. The plane's mangled but largely intact tail section was torn from the fuselage and came to rest on a nearby road.
State TV said the bodies of some of the victims were so badly burned that they could not be identified. They will be handed over to relatives after DNA tests are carried out to determine their identities, it said.
Eyewitness Hassan Molla said he heard a roaring sound as the plane came in low overhead, one wing tilting.
"There was no smoke or anything. It was absolutely sound and in good condition" before the crash and what appeared to be multiple explosions, he said.
An official for Sepahan Air told The Associated Press from the central city of Isfahan that the carrier is affiliated with the Iran Aircraft Manufacturing Industrial Company, also known as HESA. The airline was set up in 2010 and has not had any previous crashes, said the official, who refused to provide his name.
HESA has ties to Iran's Ministry of Defense and is the company that assembles the IrAn-140.