An international team of investigators piecing together a criminal case over the shooting down of Malaysia Airlines Flight 17 over Ukraine say evidence suggests links between Russia and separatists in the region were closer than previously believed.
The Joint Investigation Team (JIT) issued a fresh appeal for witnesses as it revealed details of secure communications between Russian officials and rebels in the Donetsk People's Republic (DPR) rebel group in eastern Ukraine.
In June, the investigators announced that they had charged four people, including three Russians, with murder over their alleged roles in the downing of Flight MH17 in July 2014.
All 298 passengers and crew on board the flight between Amsterdam and Kuala Lumpur were killed.
Investigators say their probe has revealed that "Russian influence on the DPR went beyond military support".
"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.
"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."
The suspects in the case 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 probably be tried in their absence.
Russia has repeatedly denied involvement in the downing of the plane.
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 on Thursday they are 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.