Dutch Prime Minister Mark Rutte wants “maximum cooperation” from Russian President Vladimir Putin in the investigation into the downing of Malaysia Airlines Flight MH17. Rutte reportedly spoke to Putin at the high-level Asia-Europe, or ASEM, summit which began on Thursday in Milan, and he also made the demand for cooperation on Twitter late Thursday.

The investigation into the MH17 disaster and the recovery of the bodies from the crash site has been moving at a slow pace due to the ongoing conflict between Ukrainian government forces and pro-Russian separatists. The Boeing 777-200 was carrying 298 people on board, mostly Dutch nationals, when it crashed on July 17. It is believed to have been brought down by a surface-to-air missile fired by pro-Moscow rebels with access to Russian arms and ammunition.

“It is an emotional subject and of course I am angry at all parties who have made it impossible to start work in at the crash site,” Rutte wrote on his Facebook page, according to Agence France-Presse. “But it’s now up to us to reach our goal. I’ll use every opportunity to highlight the issue,” he reportedly added.

Dutch forensic experts had called off an investigation due to the ongoing fighting and the lack of proper access to the crash site in eastern Ukraine. On Monday, four Dutch experts returned to the crash site to search for more human remains.

A total of 272 bodies have so far been identified by the Netherlands. On Thursday, the bodies of three Australian children who were aboard the plane, were reportedly returned to their native country for burial.

A preliminary report of the investigation into the crash, released in September by the Dutch Safety Board, stated that the jetliner broke apart in mid-air after being hit by “a large number of high-energy objects that penetrated the aircraft from outside.”