Aleksandr Zakharchenko told the BBC the investigation into the disaster, in which flight MH17 was shot at over Ukraine last year, "hadn't been carried out properly at all".
Meanwhile, Russia's aviation chief called on the United Nations aviation body to open a fresh investigation on Wednesday.
The West and Ukraine say the rebels brought down the Malaysian Airlines Boeing 777, but Russia blames Ukrainian forces.
The plane - flying from Amsterdam to Kuala Lumpur - crashed at the height of the conflict between government troops and pro-Russian separatists in July last year.
A final report into the disaster was released on Wednesday after a 15-month investigation by an international team led by the Dutch Safety Board.
Most of the victims were Dutch - 196, including some with dual nationality. The other passengers and crew were nationals from 10 countries.
The report found a Russian-made Buk missile had hit the front left of the plane, causing other parts to break off. Experts say both Russian and Ukrainian armies possess these types of missiles.
But Mr Zakharchenko, leader of the self-proclaimed Donetsk People's Republic (DNR), denied on Wednesday that his forces had possessed Buk missile launchers and criticised the board, questioning why it did not disclose to whom the missile belonged or the location from which it was fired.
Under rules governing international crash investigations, the Dutch board did not have the authority to apportion blame.
"Why were the Malaysians not given access? Why didn't they collect all the wreckage? They still haven't collected all the wreckage," he told the BBC.
The unstable security situation in the east of Ukraine hampered efforts to retrieve debris and bodies in the immediate aftermath of the disaster.
- BBC
