TEHRAN, Iran (CNN) -- An Iranian airliner that crashed Wednesday, killing all 168 passengers and crew, plunged into the ground and disintegrated on impact, according to a security official.
Debris from the plane was littered around the crash site.
Images of the crash site show a smoldering crater scattered with charred pieces of the plane and tattered passports.
Ten members of the country's youth judo team were aboard the Caspian Airlines plane, said several sources, including Iran's Press TV. The government-backed network said the dead included eight athletes and two coaches.
The plane "disintegrated into pieces," said Col. Masood Jafari Nasab, security commander of Qazvin, the city nearest to the crash site in northwestern Iran.
"The aircraft all of a sudden fell out of the sky and exploded on impact, where you see the crater," a witness told Press TV from the crash site. Watch images of the crash site »
The plane's flight data recorder and cockpit voice recorder have been found, state television reported late Wednesday.
The crash was at least the fifth major airline accident in the world this year, following crashes of planes flown by Colgan Air, Turkish Airlines, Air France and Yemenia Airways. A US Airways pilot managed to land his plane safely on the Hudson river in New York City in January, with no major injuries, after the plane lost power.
But aviation safety expert John Wiley said there is no reason to fear air travel in general, and no single airline or aircraft is particularly dangerous.
The three most recent crashes -- in which a total of 548 people died -- involved different planes, flown by different airlines, in different stages of flight, he said.
Caspian Airlines Flight 7908 -- a Russian-made Tupolev Tu-154M plane -- went down near the village of Jannatabad near Qazvin at 11:33 a.m. (2:03 a.m. ET) Wednesday, Press TV reported.
Conversations between the pilot and the ground were normal and did not indicate any technical problems, the network's Web site reported, citing the managing director of Iran's airport authority without naming him.
Some witnesses say the plane caught fire before crashing, Press TV said.
The plane descended very quickly, Wiley told CNN, but it may have been circling, trying to land, rather than plummeting to the ground.
Qazvin Police Chief Hossein Behzadpour and Mohammad Reza Montazer Khorasan, the head of the disaster management center in Iran's health ministry, both confirmed that all 168 people on board died, Press TV reported.
The U.S. State Department, in a statement, extended its condolences to the victims. Department spokesman Ian Kelly said officials were working to determine whether any Americans were on board.
Aviation analyst Kieran Daly told CNN that many aircraft operating in Iran are aging Tupolevs, some dating back to the 1970s.
He described Tupolevs as "workhorses of the old Soviet aviation system."
But he said the Caspian Airlines fleet is based on a slightly newer design, dating to the late 1980s and early 1990s.
Pictures from the scene were "consistent with a high-speed impact," he said. But he added that there could be large debris not seen on television, and that could change his analysis. Watch Daly talk about the crash »
A team of investigators from the Russian Interstate Aviation Committee is flying to the crash scene to join the investigation, the agency said in a posting on its Web site. They will work alongside Iranian aviation authorities, the agency said.
An agency official declined to comment further, saying the plane was operated by an Iranian company and nothing is known about it.
A Tupolev representative told CNN the manufacturer will not comment until the aviation committee releases its report on the crash.
The Tupolev 154 is essentially banned in the West because it does not comply with European noise and pollution regulations, but it has a safer-than-average accident record, Wiley said.
Wednesday's crash is the first on record for Caspian Airlines, which was founded in 1993, he added.
The Iranian newspaper Hamshahri reported that the plane was flying from Tehran and was headed to Yerevan, Armenia.
The semi-official Mehr news agency listed the names of 153 passengers and 15 crew members. At least 42 of the names appeared to be Armenian, but it was not clear if they were from the former Soviet republic or if they were ethnically Armenian citizens of Iran.
The plane crashed 16 minutes after takeoff, said the newspaper, quoting a spokesman from Iran's civil aviation organization. See a map of the crash location »
That would have put the flight in one of the safest stages of travel, according to International Air Transport Association data. Only about 5 percent of accidents take place during the phase called en-route climb, 16 to 20 minutes into a flight, when a plane climbs to a cruising altitude of 35,000 feet. About half of accidents take place during landing.
Iranian President Mahmoud Ahmadinejad expressed his condolences to the victims' families, as did the European Union. Russian President Dmitry Medvedev sent his sympathies to the presidents of Iran and Armenia, the Kremlin said.
Qazvin is the largest city in the province of Qazvin and is its capital, with an estimated population of 330,000.
It is about 90 miles (145 kilometers) northwest of Tehran, the capital of Iran.
The last crash in Iran involving a Tupolev plane occurred in 2006, according to the Web site airdisaster.com.
That crash occurred on an Iran Air Tour flight from the port city of Bandar Abbas; it crashed and caught fire during landing, the Web site reported.
Twenty-nine of the 147 people on board died in that crash.
CNN's Shirzad Bozorgmehr, Maxim Tkachenko in Moscow, Russia, and Ayesha Durgahee in London, England, contributed to this report.