Details of phone intercepts have been released which investigators say reveal Moscow's influence over pro-Russian rebels accused of downing a Malaysia Airlines flight over Ukraine.
MH17 was shot out of the sky in July 2014 over territory held by pro-Russian separatists in eastern Ukraine as it flew from Amsterdam to Kuala Lumpur.
All 298 on board died, including 38 Australians.
The joint investigation team (JIT) probing the crash has said a missile that hit the airplane originated from Russia's Kursk military base, not far from the Ukrainian border.
The JIT charged three Russians and a Ukrainian with 298 murders in June.
Investigators said on Thursday the pro-Russian rebels in the self-declared Donetsk People's Republic (DPR), who allegedly fired the missile, had been in closer contact with authorities in Moscow than previously assumed.
"Recent analysis of witness statements and other information revealed that Russian influence on the DPR went beyond military support and that the ties between Russian officials and DPR-leaders appear closer," the JIT said.
A series of telephone call intercepts was released on the investigation's website along with an appeal for witnesses to come forward.
A Ukrainian rescue worker passes wreckage of the Boeing 777, Malaysia Arilines flight MH17 in 2014. Source: AAP
"These telephone numbers were used on a daily basis to discuss administrative, financial and military matters in the DPR. The JIT wants to know by whom these telephone numbers were used," it said.
AFP joins witness search
Australian Federal Police have joined the international search for fresh for witnesses to the crash.
Officers want to know who commanded deployment of the surface-to-air missile that downed the plane and information about separatists in the city of Donetsk.
"We are committed to seeking justice and I urge anyone with information on this matter to come forward," AFP Assistant Commissioner Peter Crozier said on Friday.
Four suspects were charged in June with causing the crash and murdering all of those on board.
AFP Commissioner Peter Crozier says Australian officers are helping to find fresh witnesses. Source: ANP
The JIT statement named Sergey Aksyonov, the Russian-appointed leader in Russian-annexed Crimea, and Vladislav Surkov, a senior aide to Russian President Vladimir Putin.
Those Russian officials had contact with self-proclaimed prime minister in the DPR Alexander Borodai and self-proclaimed defence minister Igor Girkin, a defendant in the case, it said.
"The indications for close ties between leaders of the DPR and Russian government officials raise questions about their possible involvement in the deployment of the (missile), which brought down flight MH17 on 17 July 2014," the JIT said.
Three former rebel leaders have previously told Reuters that Surkov decided how the pro-Moscow administration of eastern Ukraine was run and who got what jobs there, challenging Kremlin denials that it calls the shots in the region.
Both the rebels and Moscow have repeatedly denied any involvement in the downing of MH17.
Russia also denies Western accusations that it sent ground troops as well as weapons and funding to the rebels in eastern Ukraine.
The Dutch-led investigative team has previously named Russians Sergey Dubinsky, Oleg Pulatov and Igor Girkin, and Ukrainian Leonid Kharchenko as suspects in the downing of the plane.
The four suspects are due to go on trial in absentia in a Dutch court next March.
