Dutch-led investigators have released new recordings of intercepted telephone calls that show separatist leaders in Ukraine requesting military support and political guidance from Russian political figures in the period before the shooting down of a Malaysian airliner that killed all 298 people on board.

Those caught on tape allegedly include Vladislav Surkov, a political aide to Vladimir Putin, whom separatist leaders have called “our man in the Kremlin”. Security officials in the audiotapes also refer to “a mandate” from the Russian defence minister, Sergey Shoigu, to change east Ukraine’s military hierarchy and coordination with the FSB director, Alexander Bortnikov, to deliver military aid, apparently including night-vision equipment and ammunition.

The recordings show how Russian political and military officials exerted control over day-to-day policy in separatist-held Ukraine. “Recent analysis of witness statements and other information revealed that Russian influence on the DPR [the self-declared Donetsk People’s Republic] went beyond military support and that the ties between Russian officials and DPR leaders appear closer,” the Dutch-led joint investigative team (JIT) said.

In one of the recordings, Alexander Borodai, the former separatist leader, is heard saying: “I’m carrying out orders and protecting the interests of one and only state, the Russian Federation. That’s the bottom line.”

A phone used by Borodai was switched off on Thursday afternoon. He has previously said he was in touch with Surkov while he was the top separatist official in east Ukraine, but has denied any role in the shooting down of MH17 in 2014. Russia has also denied it played any role in the tragedy.

The Ukraine conflict has cost more than 14,000 lives and played a central role in impeachment proceedings in Washington, where Donald Trump has been accused of withholding crucial military aid from Ukraine in exchange for an investigation into the family of his political rival, Joe Biden.

Facebook Twitter Pinterest People walk among the debris at the crash site of MH17 in July 2014. Photograph: Dmitry Lovetsky/AP

In a 3 July conversation released by the investigation, Surkov also told Borodai that Russia would soon send “combat-ready” reinforcements under an official, Vladimir Antyufeyev, who was shortly after given a senior administrative position.

Dutch officials also said separatist leaders had been issued with secure telephones provided by the Russian security service.

If confirmed, the tapes would provide additional documentary evidence that the Kremlin had direct control over the separatist leadership and managed the transfer of a BUK anti-aircraft system used to down a passenger jet in the most shocking atrocity of Ukraine’s five-year war.

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While earlier releases focused on those tied directly to the Buk anti-aircraft missile system likely to have been used in the attack, Thursday’s release focused on “the military and administrative hierarchy who enabled the shooting down of MH17 in eastern Ukraine”, according to the JIT.

While Russia was in control, bureaucracy and parallel chains of command remained a problem. In one of the intercepts, two fighters from separate units discuss how their orders come from the FSB and the GRU, Russia’s federal security service and its military intelligence agency, respectively.

In another call, Surkov tells Borodai that he cannot yet remove a separatist commander nicknamed Demon because of one high-ranking official. “If I were a minister, I’d resolve it,” Surkov says.

In June, the JIT named four Russian-backed separatists as their first suspects. They include the former separatist commander Igor Girkin and all are believed to be living in Russia or Crimea, the peninsula annexed by Russia in 2014. Their first court session will be held in March 2020.

Investigators have already used audio recordings and photographs from social and mass media to chart the transfer of the Buk missile system from Russia into Ukraine and back. In June, Russia released a phone intercept with Surkov fielding requests for military aid from Borodai just days before MH17 was shot down.

In total, 193 Dutch citizens were killed in the crash, along with 43 Malaysian and 27 Australian citizens.