Two Ukrainian fighter jets were shot down in rebel-held eastern regions, the country's defence ministry said Wednesday.
"We have information about the downed fighter jets; now we are investigating the circumstances of the incident," Alexei Dmitrashkovsky, a spokesman for the ministry, told reporters.
Dmitrashkovsky later wrote on his Facebook page that the pilots of the jets had parachuted, but their whereabouts remained yet unknown, according to Xinhua.
The incident came less than a week after Malaysia Airlines flight MH17, a Boeing 777 en route from Amsterdam to Kuala Lumpur, crashed near the eastern Ukrainian city of Donetsk, killing all 298 people on board.
The restive Donetsk and Lugansk regions in eastern Ukraine are now under the control of insurgents, who are demanding independence from Kiev.