A Ukraine Security Council spokesman said that the black box flight recorders from downed Malaysian airliner MH17 had not been handed over and that he had no information about them.
Separatist rebels in eastern Ukraine are reportedly trying to destroy evidence at the site of the disaster.
Meanwhile a team of Malaysian experts have arrived in Kyiv to help Ukraine with the investigation.
The delegation is comprised of 132 members including forensic and dental identification experts, and civilian aviation representatives.
The group will work in close cooperation with the Ukrainian authorities.
The first international monitors from the Organisation for Security and Cooperation in Europe (OSCE) arrived on Friday at the site in Ukraine where the plane came down.
They found a horrific scene with dead bodies strewn across the ground.
Separatist militiamen hindered the progress of the OSCE observers and chased them away.
“Listen to me carefully: I am not subordinate to your Kyiv and your [Ukrainian President Petro] Poroshenko,” one balaclava-wearing militia commander told them.
“So be so kind to follow my orders. You are on the territory of Donetsk People’s Republic,” he continued.
The disaster scene is spread over 20 square kilometers of contested ground in eastern Ukraine amid a conflict in which some analysts say both sides have interests that may outweigh a desire to uncover the truth.
The 30-strong OSCE delegation only had time for a partial and superficial inspection before leaving.