THE HAGUE, Netherlands -- Researchers from the British-based group Bellingcat have published a report that, for the first time, establishes what they say is the involvement of a high-ranking Russian military intelligence officer in connection with the downing of Malaysia Airlines Flight 17 (MH17) over eastern Ukraine in 2014.
The May 25 report comes a day after the Dutch-led international Joint Investigative Team (JIT) said it had concluded the Buk missile that downed the MH17 was fired by Russia's 53rd Antiaircraft Missile Brigade from separatist-controlled territory in eastern Ukraine.
Meanwhile, the Dutch government said on May 25 that the Netherlands and Australia will hold Russia legally responsible for shooting down MH17 and the deaths of all 298 people on board.
"The government is now taking the next step by formally holding Russia accountable," Dutch Foreign Minister Stef Blok said, adding that holding a nation-state responsible for a breach of international law would involve "a complex legal process."
Blok called on Russia to "accept its responsibility and cooperate fully with the process to establish the truth and achieve justice for the victims of flight MH17 and their next of kin."
The European Union, NATO, the United States, and other Western countries joined Blok's call, but Moscow continued to deny having anything to do with the downing of the civilian passenger plane, despite mounting evidence of Russian involvement.
Russian Foreign Minister Sergei Lavrov responded to Blok's call by accusing the Netherlands of speculation to "achieve political goals."
The Kremlin also insists it has not intervened to support pro-Russia separatists in eastern Ukraine, despite compelling evidence that Moscow has provided military, economic, and political support for the separatists in their war against Ukrainian government forces.
But Bellingcat said on May 25 it had "identified conclusively" that 50-year-old Russian military officer Oleg Ivannikov was in charge of military operations in eastern Ukraine when the MH17 was shot down over separatist-controlled territory on July 17, 2014.
The research group described Ivannikov as being on active duty in eastern Ukraine as an officer of the Main Intelligence Directorate (GRU) of the General Staff of the Russian Defense Ministry.
Bellingcat said Ivannikov held the post during an "undercover deployment" into eastern Ukraine that began during the first half of 2014 and that he remained in eastern Ukraine until at least 2015.
The research group also said Ivannikov "coordinated and supervised the military activities of Russian militants, pro-Russia separatists," and contingents of a "private army" from "Wagner group" -- a Russian paramilitary organization reportedly associated with Yevgeny Prigozhin, a Russian oligarch and close associate of President Vladimir Putin.
"Ivannikov also supervised the procurement and transport of weapons across the Russia-Ukraine border," Bellingcat said. "He held these functions at the time of the downing of MH17" in July 2014.
According to the Bellingcat report, Ivannikov was known by militants and separatists under his command in eastern Ukraine's Luhansk region as Andrei Ivanovich and under the radio call name "Orion."
The JIT has been seeking the identity of the person known as Andrei Ivanovich, with the call sign "Orion," in connection with its international criminal investigation into the MH17 downing.
Bellingcat said that in addition to his undercover deployment in eastern Ukraine, Ivannikov had previously worked as a GRU agent to support separatists in Georgia's breakaway region of South Ossetia.
The Bellingcat report said Ivannikov had used the alias Andrei Ivanovich Laptav from 2006 through 2008, when he was the minister of defense and emergencies in the self-declared government of the breakaway region.
"This is somebody who has a long history of operating proxy wars on behalf of the Russian government,"Bellingcat founder Eliot Higgins told RFE/RL on May 25. "What this helps us do is...identify the command structure and how heavily involved the Russian government was. And we can see with this report, our earlier reports, and reports on other subjects around Ukraine that the Russian government was extremely heavily involved. And now we have the names of individuals who commanded things."
Russian Denial, Western Condemnation
Russia and pro-Russia separatists deny shooting down MH17 and have offered several other theories to explain the tragedy, all of which have been rejected by the JIT.
The JIT comprises investigators from Australia, Belgium, Malaysia, the Netherlands, and Ukraine.
Kremlin spokesman Dmitry Peskov said Russia had not been a fully-fledged participant in JIT's investigation and could not therefore trust its findings.
WATCH -- The Downing Of MH17: What Happened?
Peskov also said he could not comment about the Bellingcat report, saying he was "not familiar with its materials" and did not know "on what basis those conclusions were made."
But the European Union foreign-policy chief Federica Mogherini and NATO Secretary-General Jens Stoltenberg on May 25 both called on Russia to "accept its responsibility and to fully cooperate with all efforts to establish accountability."
"The downing of MH17 was a global tragedy, and those responsible must be held accountable," Stoltenberg said.
Separately, the NATO chief told RFE/RL that members of the military alliance will address a wide range of issues during a session of the NATO-Russia Council planned for May 31, including "the challenges we see with increased military activity along our borders."
"What happened over Ukraine with the downing of MH17 reflects the dangers we see when there are a conflict and increased military activities close to our borders," he said.
U.S. State Department spokeswoman Heather Nauert said it was time for Russia to "acknowledge its role in the shooting down of MH17 and to cease its callous disinformation campaign."
Britain's Foreign Secretary Boris Johnson also said Russia "must now answer for its action in relation to the downing of MH17."
"The Kremlin believes it can act with impunity," Johnson said in a statement. "This is an egregious example of the Kremlin's disregard for innocent life," Johnson said, noting that 10 British citizens were killed in the shoot down.
Kurt Volker, the special U.S. envoy for Ukraine, said on May 24 that the JIT's latest report was "very significant" because it underlines "the lack of ambiguity that there is indeed a direct responsibility in Russia."
"We need Russia to turn the corner here and decided to make peace," Volker said.