Moscow continued to deny involvement in the destruction of Malaysia Airlines Flight 17, even as an international team of investigators said Thursday that detailed analysis of video images and photos has unequivocally established that the Buk missile that brought down the plane over eastern Ukraine nearly four years ago came from a Russia-based military unit.

"Not a single anti-aircraft missile of the Russian armed forces has ever crossed the Russian-Ukrainian border," Russia's Defence Ministry said in a statement Thursday.

The ministry further suggested that many of the images investigators used to trace the path of the Buk launcher came from social media and were likely doctored or altered.

Russian Duma Deputy Yuri Shvytkin was quoted by Russian media as mocking the assertion of the five-country investigation team that it has established a clear "fingerprint" of the precise launcher used in the attack, suggesting it was "fake news."

Fred Westerbeke, chief prosecutor of the Dutch prosecutor's office, presents interim results in the ongoing investigation. Suspects were not publicly identified, but investigators said a list of persons of interest has been reduced over the past two years. (Francois Lenoir/Reuters)

The Joint Investigation Team (JIT) report Thursday made the clearest link yet to the involvement of Russian military in the deadly missile strike.

Prosecutors said they have presented their findings to Moscow and are seeking answers. The international team running the criminal investigation appealed for help from witnesses who can testify about the involvement of the Russian military's 53rd anti-aircraft missile brigade based in the city of Kursk.

The website Vesti.ru, part of the consortium of state media outlets in Russia, tiptoed around the most damning parts of the JIT's report, the coverage making no reference to the fact that investigators had named a Russian military unit as the source of the missile.

Instead, the website suggested that many of the findings had already been reported in the media that "several dozen people" are considered suspects without referencing that all or some would be members of the Russian anti-aircraft brigade.

Dutch prosecutor Fred Westerbeke said the JIT is not yet ready to name suspects, but added: "I can say that we are now entering the ... last phase of the investigation. When we will be ready, it is not possible to say at the moment because there is still a lot of work to do."

Westerbeke said the new conclusion raised new questions, "such as the question about how actively involved the brigade itself was in bringing down Flight MH17."

The Boeing 777 passenger jet was headed from Amsterdam to Kuala Lumpur, Malaysia, when it was blown out of the sky over eastern Ukraine on July 17, 2014.

All 298 passengers and crew were killed, a 24-year-old Canadian man among them. Victims from more than 30 nationalities were on the flight: 196 were Dutch, 42 Malaysian and 27 were Australians.

Debris at the crash site of Malaysia Airlines Flight MH17 is shown near the village of Hrabove in the Donetsk region of Ukraine on July 21, 2014. (Maxim Zmeyev/Reuters)

Prosecutors said in 2016 that the plane was shot down by a Buk missile fired from territory controlled by Russia-backed rebels, using a mobile launcher trucked in from Russia and hastily returned there. Thursday's presentation went a step further by identifying the exact unit allegedly involved and more details of the rocket involved.

Investigators also displayed parts of the engine casing and exhaust system of a Buk 9M38 series missile recovered from eastern Ukraine and showed photos of a unique serial number on the missile. Team members said that careful analysis of video and photos from social media traced the journey of the Russian missile convoy into Ukraine and identified the missile launcher system.

The displayed missile's serial number gave them a "fingerprint" identifying it and where it was made but investigators said they could not yet say with certainty that it was the exact missile used to down MH17.

"All findings from this forensic investigation confirm the earlier conclusion of the JIT that Flight MH 17 was shot down by 9M38 series missile," said Jennifer Hurst of the Australian Federal Police.

In the aftermath of the downing of the jet, Russian state media floated a number of conspiracy theories that attempted to spread disinformation about the incident.

In one case, a Spanish-born man who claimed to be on air-traffic-control duty in Kyiv at the time claimed to have seen the signatures of Ukrainian jets on radar, feeding the Russian conspiracy that Ukraine was behind the incident.

The man was later exposed by investigative journalists as a fraud who was never near an air-traffic-control tower. Nonetheless, Kremlin-supported media outlets for years repeated the bogus claims about the Ukrainian jets.

Russia rejected international tribunal

In a written statement, Australian Foreign Minister Julie Bishop said: "That a sophisticated weapon belonging to the Russian army was dispatched and used to shoot down a civilian aircraft should be of grave international concern. We are discussing these findings with our partners and considering our options."

Ultimately, any suspects identified and charged will be prosecuted in Dutch courts — if they can be arrested and brought to trial.

Relatives of victims of the flight embrace during the revealing of a national monument for the MH17 victims in Vijfhuizen, The Netherlands on July 17, 2017. (Remko de Waal/Pool via AP)

Russia used its veto to block a UN Security Council resolution seeking to create an international tribunal to oversee criminal complaints stemming from the incident.

Dutch prosecutors said in September 2016 that 100 "persons of interest" had been identified in the investigation; on Thursday the team said the list of possible suspects has been reduced to several dozen.

Dutch Foreign Minister Stef Blok welcomed the newly released findings.

"This is an important piece of the puzzle," Blok said. "I am very impressed by the evidence that has been collected."

Netherlands Prime Minister Mark Rutte said he was cutting short a visit to India so he could chair a cabinet meeting to discuss the findings.

His Belgian counterpart, Didier Reynders, called on all countries to co-operate fully with the investigation "so that those responsible can be brought to justice."