BRUSSELS — Senior Kremlin officials were directly involved in the day-to-day affairs of rebels in eastern Ukraine as the conflict there worsened in 2014, prosecutors investigating the downing of a Malaysian airliner that year said Thursday.

There has been little doubt that Russia was deeply involved in the conflict, despite Kremlin denials: Western journalists saw Russian troops move across the border into Ukraine and witnessed Russian troops operating on the ground. And during a key stretch in summer 2014, the rebels’ top leaders were Russian.

But the recordings and transcripts of intercepted phone calls made public Thursday offered a new level of detail about Kremlin involvement in eastern Ukraine as rebels struggled to set up the institutions of a breakaway state, press their advantage with Kyiv and manage the fallout from the July 2014 downing of Malaysia Airlines Flight 17.

The conflict is still ongoing — and is featuring prominently in U.S. impeachment hearings, as Congress investigates whether President Trump conditioned U.S. military aid for Ukraine on the country investigating his political opponents.

Western investigators say the Malaysia Airlines plane was taken down by a Russian-built missile fired from rebel-held territory, killing all 298 people aboard. The intercepted calls were released by the Dutch-led investigators. The Washington Post could not independently confirm the calls’ veracity.

“The rebels used secure means of communication. A number of these seemed to be provided by the Russian Federation and, moreover, used by Russian top officials in their contact with the fighters,” said David Taylor, a senior investigations officer with the Australian Federal Police, who is working with the international inquiry.

Maria Zakharova, a spokeswoman for the Russian Foreign Ministry, said the international investigation presupposed Russian guilt from the outset, and was now tasked only with “juggling” evidence that “would testify in favor of the chosen tactic of accusation,” Interfax reported.

In one of the recordings, Alexander Borodai, the then-leader of the rebels, can be heard telling an unidentified person: “I’m carrying out orders and protecting the interests of one and only state, the Russian Federation. That’s the bottom line.”

In a call on July 3, 2014, Kremlin aide Vladislav Surkov — who has been Russia’s point person on eastern Ukraine — told Borodai that Russian fighters “were departing for the south to be combat-ready,” mentioning a “certain Antyufeyev.” A week later, a man named Vladimir Antyufeyev gave a news conference in the rebel capital of Donetsk that he had just arrived from Russia and that he planned to take over security and internal affairs in the aspiring breakaway statelet.

Other phone calls between rebels refer to “special phones, you cannot buy them. They are gotten through Moscow. Through FSB,” Russia’s intelligence agency. Others refer to cash support from Russia and a request from Borodai to a Russian cellphone number that “our helicopters” carry out raids.

And, in conversations among themselves, the rebels talked about how a top Russian general had delivered equipment to them on the order of “the person beginning with ‘Sh.’ Do you know him?”

“No, I do not,” the second person said.

“Well, Shoigu. Shoigu,” the first person said, referring to Russian Defense Minister Sergei Shoigu.

The international group of investigators, known as the Joint Investigative Team, said that it had published the calls in the hopes of securing witnesses who would tell them more about the details.

Over the summer, they issued indictments for several of the top rebel commanders at the time of the plane’s downing.