Russia on Wednesday accused Ukraine of manipulating data held by its air traffic authorities concerning the crash of Malaysia Airlines flight MH17 last week.
"According to the latest information, Ukrainian security forces, without notifying international organisations, are engaged in some secret work with the databases and personnel of Ukrainian air traffic services, both military and civilian," foreign ministry spokesman Alexander Lukashevich said in a statement.
"That clearly goes against the goal of an objective and unbiased investigation," he added.
Instead of helping the probe into the crash in eastern Ukraine that killed all 298 people on board of the Boeing 777, Kiev is "planting absurd, unfounded accusations against Russia on a daily, hourly basis," Lukashevich said.
Moscow has faced international fury after allegations, including by the United States, that the plane was shot down with a Russian-made missile from a mobile launcher deployed in an area controlled by pro-Russian separatists.
On Monday the Russian defence ministry hotly denied that any such equipment was provided to the rebels by Russia, and alleged that the Boeing could have been diverted from its designated route by Ukraine's air traffic controllers, hinting at foul play.
Among other theories circulated by Russian officials and media are that the plane was brought down by an air-to-air missile launched from a Ukrainian warplane, or a Ukrainian missile system on the ground.