Ukraine's spy chief says he has proof that the missile that downed flight MH17 came from a Russian-operated missile launcher that has since been moved back onto Russian soil.
He said they probably thought they were aiming at a military target.
"We have proof [the attack] was planned and it was committed with the participation of the Russian Federation, representatives of the Russian Federation," said Vitaly Nayda, Counter-Intelligence Chief at the Ukraine Security Service.
"All Russian media is lying, it's cynical propaganda," Nayda said. "They are trying not to be responsible for this.
"But we have evidence. Obvious evidence."
He shared with media in Kiev some of the information the Ukraine security service had gathered, from phone intercepts and from agents within the region controlled by the rebels.
He showed a photograph which he said was a BUK-M1 system identified on the streets of Donetsk city - near the crash site - on July 17.
Among the members of the team operating the missile system were Russian citizens, Nayda said.
Phone calls intercepted by Ukraine revealed the BUK was intended to join a column of separatist fighters. Nayda showed a photograph of the column including a tank and a truck carrying the BUK-M1 system.
He also showed a photograph taken at the time of the plane being hit, showing the missile's launch plume - allowing them to identify the launch area, near the village of Snizhne and close to the plane's crash site.
The area was under separatist control at the time, Nayda said. He would not identify the precise site "in the interests of the investigation" - he said Ukraine agents were trying to access the site but "it's impossible to get to the place now".
"There is no doubt that terrorists knew that they launched a missile against a plane that was higher then 10,000m," he said.
He showed another photograph of the BUK-M1 system en route to the Russian border soon after the plane was shot down.
The photo showed that one missile was missing from the launching pad.
"Russian side told them to put that system outside of Ukraine," he said. "Russians gave an order to terrorists to take from Ukraine all BUK-M1 systems - there were many of them, not one."
At 2am (local time) on Friday July 18, about 8 hours after the plane came down, in a region of Ukraine near the Russian border, two big trucks each carrying a BUK system - one with a missing missile, were seen heading for Russia.
At 4am on Saturday morning three more such trucks moved over the border into Russia. One had a BUK-M1, one was empty, and the third carried a tracking module that runs the system.
"Russia is trying to hide its terrorist activity," Nayda said.
"(Ukrainian) rebels cannot operate the very sophisticated and high-technique missile launcher BUK-M1. To operate BUK-M1 you need to have education, military education, and to be well-trained.
"We know for sure the team was Russian, they were Russian citizens operating BUK-M1 and they came from the territory of the Russian Federation together with the missile launcher.
"We documented negotiations between terrorists that directly told us. We got information directly from those conversations that three Russians, three Russian military personnel came together with BUK-M1 to the territory of Ukraine. It is direct evidence."
On June 29 the separatists in eastern Ukraine announced to Russian media they have gained access to a BUK-M1 land-air missile system - a system capable of hitting a plane at MH17's altitude.
They claimed to have captured it from a Ukrainian army base.
However, the base had only contained one BUK-M1 which had been disabled on March 3, and had no missiles, Nayda said. The remains of that launcher were still on the base.
There was a "hint" of information from agents in the field on July 14, three days before the attack, that the launchers had arrived on Ukraine territory from Russia.
But the presence of three launchers had only been confirmed after the attack when they were returning to Russia, Nayda said.
Nayda said Ukraine has passed all its evidence and data on to international allies, including the US and other countries who had lost citizens in the crash.
He called on the international community to ask Russia how it would help the investigation of the attack, and demanded that Ukraine be allowed to interview Russian personnel who launched the missile.
He said Ukraine would only be able to show whether the missile had been launched on purpose at a civilian flight once those responsible had been arrested.
"We know for sure the terrorists have the plan to shoot down every military plane, even cargo plane, even helicopter or jet fight(er) in the air over the territory of Donetsk and Lugansk region," Nayda said.
"I cannot confirm what they aimed at the moment when they launched the missile. They knew definitely that the height was more than 10,000m but they also knew that probably it was Ukrainian cargo plane, military plane that was delivering cargo to Donetsk or Lugansk region."
- Sydney Morning Herald