Pilot error and weather conditions are also being investigated as the cause of the incident, RIA Novosti reported.
"We should check all the possibilities," said Deputy Prosecutor General Viktor Voitsishen.
He noted that three people on the flight weren't registered.
The Antonov An-24 turboprop airliner, with 52 people aboard, missed the runway at the eastern Ukrainian city of Donetsk Wednesday evening. It turned upside down, broke into pieces and caught fire.
The passengers were soccer fans headed to a match against a German team.
Volodymyr Porodko, deputy chairman of Ukraine's Security Service, said investigators were checking whether flammable or explosive items were on the plane.