Kiev has undeniable evidence that Russia was behind the shooting down of a Ukrainian military transport aircraft, a senior security official said Tuesday.

"President (Petro Poroshenko) ordered completing investigation till the end of today, with all maps and sectors to be prepared," Valentin Nalivaichenko, deputy head of the Ukrainian Security Service, told reporters.

He did not specify the "undeniable evidence," but said it would be presented to the president later.

On Monday, an An-26 military transport plane with eight people onboard was brought down in the eastern Lugansk region. Local insurgents have claimed responsibility, saying four of its crew had been captured.

Meanwhile, Andrei Lysenko, a spokesman for the National Security and Defense Council, denied reports that the air force struck civilian targets in the town of Snezhnoye in Donetsk region Tuesday morning.

"An unidentified plane bombed the town's central street, inflicting civilian casualties and destroying several buildings," Interfax news agency quoted Lysenko as saying.

He called the airstrike a "provocation," but stopped short of pointing at who might carry out the strike.