“The rumors about the plane are completely false and no military or political expert has confirmed it,” Gen. Abolfazl Shekarchi, spokesman for the Iranian armed forces, was quoted by the semiofficial Fars news agency as saying. He said the rumors were "psychological warfare" by the government's opponents.
In Washington, a Democrat who attended a classified briefing from Trump administration officials on Capitol Hill — including Defense Secretary Mark Esper, Secretary of State Mike Pompeo and CIA Director Gina Haspel — said the briefers had no intelligence indicating the plane was shot down. The lawmaker spoke on condition of anonymity.
The plane, en route to the Ukrainian capital of Kyiv, was carrying 167 passengers and nine crew members from several countries, including 82 Iranians, at least 63 Canadians and 11 Ukrainians, according to officials. The crash just before dawn scattered flaming debris and passengers' belongings across a wide stretch of farmland.
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.
Canadian Prime Minister Justin Trudeau said 138 of the passengers were bound for Canada.. The flight also included a family of four and newlyweds, too. The manifest listed several teenagers and children, some as young as 1 or 2.
The crash ranked among the worst losses of life for Canadians in an aviation disaster. The flag over Parliament in Ottawa was lowered to half-staff, and Trudeau vowed to get to the bottom of the disaster.
“Know that all Canadians are grieving with you," he said, addressing the victims' families.
Ukraine's president Volodymyr Zelenskiy cut short a visit to Oman to return to Kyiv and said a team of Ukrainian experts would go to Tehran to help investigate the crash.
"Our priority is to find the truth and everyone responsible for the tragedy," he wrote in a Facebook statement.
Ukrainian officials, for their part, initially agreed that the 3½-year-old plane was brought down by mechanical trouble but later backed away from that and declined to offer a cause while the investigation is going on.
While the cause of the tragedy remained unknown, the disaster could further damage Boeing's reputation, which has been battered by the furor over two deadly crashes involving a different model of the Boeing jet, the much-newer 737 Max, which has been grounded for nearly 10 months. The uproar led to the firing of the company's CEO last month.
Boeing extended condolences to the victims' families and said it stands ready to assist.
Authorities said they found the plane's so-called black boxes, which record cockpit conversations and instrument data.
But given the near state of war between Iran and the U.S., it was not immediately clear whether the Iranians would share the devices with investigators from the United States and its allies or whether Tehran would invite the U.S. National Transportation Safety Board to take part.
Normally investigators from the country of the plane's origin -- in this case, the U.S. -- participate in the investigation of major crashes in other nations.
Immediately after the crash Qassem Biniaz, a spokesman for Iran's Road and Transportation Ministry, said it appeared a fire erupted in one of its engines and the pilot lost control of the plane, according to the state-run IRNA news agency. The news report did not explain how Iranian authorities knew that.
Major world airlines, meanwhile, rerouted flights crossing the Middle East to avoid danger amid escalating tensions between the U.S. and Iran, and the U.S. Federal Aviation Administration barred American flights from certain Persian Gulf airspace, warning of the “potential for miscalculation or misidentification" of civilian aircraft.
Ukraine International Airlines President Yevhen Dykhne, said the aircraft “was one of the best planes we had, with an amazing, reliable crew." The jet last underwent routine maintenance on Monday, according to the airline. As for the pilots, it said, "Given the crew’s experience, error probability is minimal. We do not even consider such a chance.”
The Ukrainian plane slammed into the ground near the town of Shahedshahr, causing fires that lit up the darkened fields before daybreak. Din Mohammad Qassemi said he had been watching the news about the Iranian missile attack on U.S. troops in Iraq in revenge for the killing of Gen. Qassem Soleimani when he heard the crash.
“I heard a massive explosion and all the houses started to shake. There was fire everywhere," he said. “At first I thought (the Americans) have hit here with missiles and went in the basement as a shelter. After a while, I went out and saw a plane has crashed over there. Body parts were lying around everywhere.”
The crash left a wide field of debris scattered across farmland, including pieces of the shattered aircraft, a child's cartoon-covered electric toothbrush, a stuffed animal, luggage and electronics.
As for the Boeing 737-800 model that went down, thousands of the twin-engine jetliners introduced in the late 1990s are in use around the world, and it has one of the best safety records among popular airliners.
The Aviation Safety Network said there have been eight fatal crashes involving the Boeing 737-800 out of nearly 5,000 built. A FlyDubai crash in Russia in 2016 killed 62 people, and an Air India Express disaster in India in 2010 left more than 150 dead.
The 737-800s have been the subject of inspections and repairs since last year, after airlines started reporting cracks in a part that keeps the wings attached to the fuselage.
Gambrell reported from Dubai, United Arab Emirates, and Koenig from Dallas. Associated Press writers Adam Schreck in Bangkok; Daria Litvinova in Moscow; Inna Varenytsia and Dmytro Vlasov in Kyiv, Ukraine; Carlo Piovano in London; and Rob Gillies in Toronto contributed to this report.