Forty-nine Ukrainian military personnel were killed when rebels shot down a cargo plane over the airport of the eastern city of Luhansk overnight, military spokesman Vladislav Seleznov said on Saturday.
Ukraine's defense ministry earlier reported separatist rebels had shot down a military transport aircraft IL-76 carrying troops and supplies.
The Il-76 aircraft carrying "military personnel, machinery, equipment and supplies" was approaching the airport in Luhansk when it came under attack by "anti-aircraft and heavy machine guns," the Ukrainian Defense Ministry said said in a statement.
Local media reported earlier that some 30 people were aboard the plane.
Violent confrontations between insurgents and the government troops have continued in the mostly Russian-speaking Lugansk and Donetsk regions since mid-April. So far, the unrest has killed more than 200 people.
The Soviet-made Il-76 can carry up to 167 soldiers with ammunition and seven crew members.