The Ukrainian prosecutor general's office says 49 people died Saturday when pro-Russian separatists shot down a military transport.
Nine crew and 40 service members were aboard the Il-76 plane when it went down early Saturday as it approached the airport at the city of Lugansk, according to a statement on the office's website.
Another official, counter-terrorism spokesman Vladislav Seleznyov, was quoted by the Interfax news agency as saying the figure was preliminary.
The prosecutor's office said a criminal investigation had been opened under anti-terrorism laws.
The Ukrainian Defence Ministry said the plane was carrying equipment and food as well as personnel.
The ministry's statement said that the rebels "cynically and treacherously" downed the plane using anti-aircraft guns and heavy calibre machine-guns. It expressed sympathy to the families of those killed "for their tragic and irreparable loss.''
An Il-76 is a four-engine jet that can be used to transport heavy gear and people.
Lugansk is in Ukraine's east near its border with Russia, an area that has seen separatists seize government buildings and declare independence after holding disputed referendums. The Ukrainian health ministry says at least 270 people have died in clashes between government forces and armed separatists, who Ukraine says are supported by Russia. Russia denies that.
Tensions between Ukraine and Russia escalated in February after pro-Russian President Viktor Yanukovych was driven from office by a protest movement made up of people who want closer ties with the European Union.
David McHugh/ Associated Press