However, Alexander Bastrykin, the chief of the federal Investigative Committee, said the jet's right engine apparently failed and caught fire as the plane was preparing to land in rainy weather.
Flight 821, operated by a subsidiary of national flag carrier Aeroflot, carried 82 passengers and six crew members, Aeroflot said. Company officials said the plane was circling at about 3,600 feet (1,100 meters) in "difficult weather conditions" - including low cloud cover and rain - when it went down.
Flight controller Irek Bikbov told state-run Channel One TV that the pilot was behaving strangely, disobeying orders to descend on the final approach and instead taking the jet to a higher altitude.
"I informed the pilot that he has reached a point where he should go down," Bikbov said in an audio recording broadcast on TV. "He confirmed he was going down but kept climbing."
Bikbov then ordered the pilot to make a second run, but instead of making the right turn he turned left.
When he asked the pilot whether things were normal on board, the pilot answered positively but his voice was strained as if under stress, Bikbov said.
"He was behaving in a strange manner and wasn't following my orders," Bikbov said. The last thing controllers heard was a scream in the cockpit seconds before the plane crashed.
The plane's flight recorders have been found, and official said it would take at least three weeks to analyze them.
Transport Minister Igor Levitin, meanwhile, said that no trace of explosives had been found on the crash site about 1,200 kilometers (750 miles) east of Moscow. He denied earlier reports that claimed the plane had exploded and allegations that it could have been brought down by a terror attack.
The plane slammed into the ground on the outskirts of this industrial city, just a few hundred meters (yards) from small wooden houses and apartment buildings. No one on the ground was killed.
The jet crashed on a railroad embankment, damaging a section of the track. Parts of the plane's fuselage reading "Aeroflot" and "Boeing" lay askew on the rails, along with clothing, life preservers and engine parts. The crash briefly disrupted traffic on a section of the Trans-Siberian railway.
Emergency workers in camouflage uniforms on Monday picked up human remains and placed them in blue bags. Grief-stricken relatives of passengers lined up to provide blood and DNA samples to help in the identification.
Aeroflot said it would pay victims' families an equivalent of US$80,000 in compensation per victim - a princely sum in a country where the average monthly salary is equivalent to about US$700.
Russia and other former Soviet republics have some of the world's worst air traffic safety records in recent years, according to the International Air Transport Association. Experts blame weak government regulation, poor pilot training and a cost-cutting mentality among many carriers.
In the past, some industry experts said meager compensations for families of crash victims have contributed to a sloppy attitude among Russia's air carriers toward safety.
"The problem isn't the planes, it's mainly about the staff and money," said Miroslav Boichuk, head of Russia's Flight Personnel Union.
Aeroflot officials have said no problems were reported with the 15-year-old jet when it was last inspected at the beginning of the year. The plane had been used by a Chinese carrier before the Aeroflot subsidiary, Aeroflot-Nord, leased it earlier this year.
Sunday's crash was the worst involving a Russian airline since August 2006, when 170 people were killed in the crash of a Tu-154 jet in Ukraine. A month earlier, an Airbus A-310 skidded off the runway in the Siberian city of Irkutsk and burst into flames, killing 125.
Sunday's crash was also the second involving a Boeing 737 in the former Soviet Union in the past month. A Boeing flying from the Central Asian nation of Kyrgyzstan to Iran crashed shortly after takeoff Aug. 24, killing 64 of the 90 people on board.
