Iranian cabinet spokesman Ali Rabiei said that such allegations “rub salt on a painful wound” for the families of the victims.
Iran has denied that a Ukrainian jetliner that crashed near Tehran on Tuesday was shot down by an Iranian missile.
In a press conference, Ali Abedzadeh, chief of Iran's Civil Aviation Organisation (CAOI). said: "One thing is for certain - that plane has not been hit by a missile."
His comments came as a video surfaced from Iran, which was verified by the New York Times and Bellingcat, that appears to show a surface to air missile striking the plane.
Earlier, Canadian Prime Minister Justin Trudeau said that intelligence from "multiple sources" showed the plane was shot down by "an Iranian surface-to-air missile". He added that it "may have been unintentional".
U.S. sources with access to intelligence reports said they increasingly believed an Iranian anti-aircraft missile downed the Ukrainian International Airlines Boeing 737, killing all 176 passengers and crew shortly after takeoff from Tehran.
British Prime Minister Boris Johnson also commented on the crash stating that there was a "body of information" suggesting the flight was shot down by a missile. Johnson again called on "all sides" to "deescalate to reduce tensions in the region".
Flight PS752 crashed just a few hours after Iran launched a ballistic missile attack against military bases housing US troops in Iraq amid a confrontation with Washington over the US drone strike that killed Iranian general Qassem Soleimani.
Eyewitnesses, including the crew of a passing flight, described seeing the plane engulfed in flames before crashing.
Iranian cabinet spokesman Ali Rabiei said late Thursday that the allegations “rub salt on a painful wound” for the families of the victims.
President Donald Trump suggested that he believes Iran was responsible and wouldn't directly lay the blame but dismissed Iran's initial claim that it was a mechanical issue.
“Somebody could have made a mistake on the other side," Trump said, noting the plane was flying in a “pretty rough neighborhood."
“Some people say it was mechanical,” Trump added. “I personally don't think that's even a question.”
The US intelligence assessment comes after a preliminary Iranian investigative report said the pilots never made a radio call for help but were trying to turn back for the airport.
Investigators from Iran's Civil Aviation Organization offered no immediate explanation.
Meanwhile, the state-run IRNA news agency quoted a Foreign Ministry spokesman as saying Iran "has invited both Ukraine and the Boeing company to participate in the investigations.” The spokesman, Abbas Mousavi, said it will also welcome experts from other countries' whose citizens died in the crash.
Iran had initially said it would not allow Boeing to take part in the probe, going against prevailing international norms on crash investigations. It later invited the U.S. accident-investigating agency to take part in the investigation.
Black boxes recovered
Ukrainian International Airlines Flight PS752 took off at 6:12 am local time on Wednesday, after nearly an hour's delay. It gained altitude heading west, reaching nearly 8,000 feet.
Eyewitnesses, including the crew of another flight passing above it, described seeing the plane engulfed in flames before crashing at 6:18 am.
The preliminary Iranian report also confirmed that both of the so-called “black boxes” that contain data and cockpit communications from the plane had been recovered, though they sustained damage and some parts of their memory was lost.
Oleksiy Danilov, secretary of Ukraine's Security Council, said officials had several working theories regarding the crash, including a missile strike.
"A strike by a missile, possibly a Tor missile system, is among the main (theories), as information has surfaced on the internet about elements of a missile being found near the site of the crash," Danilov said.
Ukrainian investigators who arrived in Iran earlier on Thursday were still awaiting permission from Iranian authorities to examine the crash site and look for missile fragments, Danilov said.
The Tor is a Russian-made missile system. Russia delivered 29 Tor-M1s to Iran in 2007 as part of a $700 million (€630 million) contract signed in December 2005. Iran has displayed the missiles in military parades as well.
Ukraine has a grim history with missile attacks, including in July 2014 when one such strike downed a Malaysian Airlines flight over eastern Ukraine, killing all 298 people aboard.
The manufacturer of the plane's engines, US-French firm CFM, declined to comment. French air accident investigators have not been asked to take part in the investigation so far.
63 Canadians onboard PS752
The plane was carrying 167 passengers and nine crew members from several countries, including 82 Iranians, at least 63 Canadians and 11 Ukrainians, according to officials. Many of the passengers were believed to be international students attending universities in Canada; they were making their way back to Toronto by way of Kyiv after visiting with family during the winter break.
Ukrainian President Volodymyr Zelenskiy said he planned to call Iranian President Hassan Rouhani about the crash and the investigation.
“Undoubtedly, the priority for Ukraine is to identify the causes of the plane crash,” Zelenskiy said. “We will surely find out the truth.”