It slammed into farmland at Khalaj Abad, in Shahriar county, about 45 kilometres northwest of the airport, according to reports on state media.
"Obviously it is impossible that passengers" on flight PS-752 are alive, Red Crescent head Morteza Salimi told semi-official news agency ISNA.
"Out of the 176 people who died, nine were flight crew members and the others passengers," Mohammad Taghizadeh, the deputy governor for Tehran province, told ISNA. Seventy were men, 81 women and 15 children, he said.
"There are currently 500 medical units on the scene" gathering bodies, he added. Emergency services spokesman Mojtaba Khaledi said the vast majority of the dead were Iranian citizens.
Just two passengers and nine crew members were Ukrainian, according to Ukraine's national security council, which is overseeing a crisis team. Ukrainian President Volodymyr Zelensky confirmed all those on board the plane were killed.
The aircraft was carrying 82 Iranian and 63 Canadian nationals, a Ukrainian minister said. The Boeing 737 was also carrying 11 Ukrainians, 10 Swedes, four Afghans, three Germans and three Britons, Foreign Minister Vadym Prystaiko wrote on Twitter.
"According to preliminary data, all passengers and crew members are dead," he wrote on Facebook.
The Red Crescent said teams were being assisted by soldiers and firefighters in the effort to recover bodies.
"After six o'clock (0230 GMT) this morning we were informed that a passenger plane crashed in the vicinity of Shahriar," said Shahin Fathi, the head of its search and rescue unit.
"All operational teams were dispatched to the area," he told state television. "Unfortunately... we haven't found anyone alive."
The crash was likely to have been caused by "technical difficulties", Press TV said, quoting Ali Khashani, spokesman for Imam Khomeini International Airport.
The Ukrainian airline whose plane crashed outside Tehran on Wednesday, killing over 170 people, said the Boeing 737 was built in 2016 and checked only two days before the accident.
"The plane was manufactured in 2016, it was received by the airline directly from the (Boeing) factory. The plane underwent its last planned technical maintenance on January 6, 2020," Ukraine International Airlines said in a statement.
"The plane caught fire after crashing," said Press TV, state television's English-language news broadcaster.
A video aired by the state broadcaster appeared to show the plane already on fire, falling from the night sky.
American airline manufacturer Boeing tweeted: "We are aware of the media reports out of Iran and we are gathering more information." The Ukrainian president warned against speculation about the causes of the crash.
"I ask everyone to keep from speculating and putting forth unconfirmed theories about the crash," Zelensky he wrote on Facebook, as he cut short a vacation in Oman and flew back to Ukraine.
Aviation expert Stephen Wright said he doubted the airliner had been downed by an Iranian missile but said the evidence suggested something "catastrophic" had taken place.
"There is a lot of speculation at the moment it has been shot down - I think that is not going to be the case at all," he said. "The aircraft was climbing... it was going up in the right direction, which means that something catastrophic has happened.
"It could be a bomb or it could be some sort of catastrophic breakup of the aircraft." Wright, a professor of aircraft systems at Tampere University in Finland, said the aircraft was quite new and not one of the the MAX models fitted with anti-stall systems that have been linked with two other recent crashes.
The crash came shortly after Iran said it fired missiles at Iraqi bases in revenge for the killing of one of the Islamic republic's top military commanders in a US drone strike on Friday.
Following the missile strikes, the US Federal Aviation Administration (FAA) said it was banning US-registered carriers from flying over Iraq, Iran and the Gulf after rocket attacks on US forces in Iraq.
"The (FAA) issues Notices to Airmen tonight outlining flight restrictions that prohibit US civil aviation operators from operating in the airspace over Iraq, Iran and the waters of the Persian Gulf and the Gulf of Oman," it said in a statement.
"The FAA will continue closely monitoring events in the Middle East." Iran launched the missiles after a US drone strike killed Qasem Soleimani, a hugely popular figure who headed the foreign operations arm of the Islamic Revolutionary Guard Corps.
Supreme leader Ayatollah Ali Khamenei vowed "severe revenge" for the assassination and declared three days of mourning following the assassination which shocked the Islamic republic.
The assassination of Soleimani set off an escalating war of words between Iran and the US.
In Tehran, President Hassan Rouhani on Monday warned Trump to "never threaten" Iran, after the US leader issued a US strike list of 52 targets in the Islamic republic.
This story has been published from a wire agency feed without modifications to the text. Only the headline has been changed.