The Ukrainian Security Service released yet another series of recordings depicting what it said are intercepted phone calls between pro-Russian separatists in eastern Ukraine that show rebels tried to keep evidence from the Malaysia Airlines plane crash, including flight data recorders, out of the hands of independent investigators on orders from Russia.

“Moscow asks where the black boxes are,” said a voice on the first of three recordings, which Ukraine’s security services identified as Alexander Khodakovsky, the leader of the pro-Russian “Vostok” battalion. “They must be under our control.”

In a second recording, the voice of Ukraine’s security service identified as Khodakovsky is more insistent that the rebels must maintain control over any evidence recovered from the crash site, especially the flight data recorders.

“Our friends from high above are very much interested in the fate of the ‘black boxes.’ I mean people from Moscow,” said the voice in a second recording. “All that you find must not come into somebody else’s hands.”

The Washington Post could not independently verify the authenticity of the recordings or the individuals identified in them. The Ukrainian Security Service said the recorded conversations took place during the evening hours on Friday – the first day OSCE monitors came to inspect the crash site.

OSCE monitors have complained that rebel guards have controlled their movements around the crash site closely since they first arrived on Friday, though an OSCE spokesman said that monitors were given wider access on Sunday than in previous days. Ukrainian officials have also accused pro-Russian rebels of destroying evidence at the crash site.

On Sunday, Donetsk rebel Alexander Borodai said that the pro-Russian separatists had recovered the plane’s black boxes and would be handing them over to the International Civil Aviation Organization.

Borodai also denied that rebels had hindered monitors’ access to the crash site.

Earlier on Sunday, the U.S. State Department released a statement saying that it believed previous Ukrainian recordings of rebels’ phone conversations were authentic. The Ukrainian Security Service has released two other rounds of recordings since the plane carrying 298 passengers crashed in the eastern part of the country.

The Security Service claimed the first round of recordings depicted pro-Russian rebels conferring about the attack on the plane and possibly claiming to have shot it down. It claimed the second set of recordings showed that pro-Russian rebels had the firepower – namely, a Buk system – that could have brought down the plane. The Post could not independently verify the authenticity of those recordings or the individuals identified in them.