THE HAGUE, Netherlands (AP) — An international team of investigators piecing together a criminal case in the July 2014 shooting down of Malaysia Airlines Flight 17 over eastern Ukraine said Thursday that evidence suggests links between Russia and separatists in the region were closer than previously believed.

The Joint Investigation Team issued a fresh appeal for witnesses and revealed details of secure communications between Russian officials and rebels in the Donetsk People’s Republic (DPR) rebel group in eastern Ukraine.

“The JIT has information that indicates that the influence of the Russian Federation extended to administrative, financial and military matters in the DPR,” the team said in a statement, adding that contacts between Russia and the rebels intensified in the first half of July 2014.

“There was almost daily telephone contact between the leadership of the DPR and their contacts in the Russian Federation,” the JIT said. “They spoke with leaders in Moscow, near the border with Ukraine and in Crimea. Communication mostly took place via secure telephones provided by the Russian security service.”

Russia has repeatedly denied involvement in the downing and accused the investigation team of bias.

At a weekly briefing in Moscow on Thursday, Russia’s Foreign Ministry spokeswoman Maria Zakharova questioned the evidence.

“What are they (the conclusions) based on? Publication of materials, some of which immediately turn out to be fake, and some of which don’t check out? We’ve been through this already,” she said.

In June, the investigators announced they had charged four people, including three Russians, with murder over the July 17, 2014, downing of Flight MH17. All 298 passengers and crew on board the Amsterdam-Kuala Lumpur flight were killed.

The suspects are due to go on trial in a secure courtroom near Amsterdam's Schiphol Airport in March, though they are not in custody and will likely be tried in their absence.

Investigators said their probe revealed that “Russian influence on the DPR went beyond military support.”

The team, made up of detectives and prosecutors from the Netherlands, Malaysia, Australia, Belgium and Ukraine, last year said it was convinced that the Buk missile system used to shoot down flight MH17 came from the Russian army's 53rd Anti-Aircraft Missile brigade, based in the Russian city of Kursk.

The team said Thursday it is looking for witnesses “who can share information about those who controlled the DPR leadership in Donetsk and commanded the deployment of the Buk” missile system.

“The indications for close ties between leaders of the DPR and Russian government officials raise questions about their possible involvement in the deployment” of the missile, the investigators said.

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Daria Litvinova in Moscow contributed.

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