KHARKIV, Ukraine (AP) — A Dutch military aircraft carrying remains of victims from the Malaysian plane disaster departed for the Netherlands Thursday and a second prepared to go, while Australia's government dispatched 50 police officers to London to prepare to join a proposed U.N. team to secure the scattered wreckage.

All 298 people aboard Malaysia Airlines Flight 17 — most of them Dutch citizens — were killed when the plane was shot down on July 17. Wreckage of the Boeing 777 fell on territory controlled by pro-Russian separatists, and U.S. officials say the plane was probably shot down by a missile, most likely by accident.

Australian Prime Minister Tony Abbott, who says he fears some remains will never be recovered unless security is tightened, has proposed a multinational force mounted by countries such as Australia, the Netherlands and Malaysia that lost citizens in the disaster.

Foreign Minister Julie Bishop was traveling with her Dutch counterpart Frans Timmermans to Kiev to seek a memorandum of understanding with the Ukraine government to allow international police to secure the area where the wreckage fell, Abbott said.

Details including which countries would contribute and whether officers would be armed and protected by international troops were yet to be agreed, Abbott said.

Bishop presented an Australia-sponsored resolution to the U.N. Security Council, approved unanimously on Monday, demanding that rebels cooperate with an independent investigation and allow all remaining bodies to be recovered.

The first bodies of the crash victims arrived in the Netherlands on Wednesday and were met by Dutch King Willem-Alexander, Queen Maxima and hundreds of relatives.

Ukraine's government said 51 containers of bodies and body parts had been cleared for Thursday's flights. At least 200 bodies were aboard the train that brought them from the crash site to Kharkiv earlier this week.

Senior U.S. intelligence officials said Tuesday that Russia was responsible for "creating the conditions" that led to the crash, but offered no evidence of direct Russian government involvement.

The officials said the plane was likely shot down by an SA-11 surface-to-air missile fired by Russian-backed separatists in eastern Ukraine. The U.S. officials cited intercepts, satellite photos and social media postings by separatists, some of which have been authenticated by U.S. experts.

Russia on Thursday brushed off the accusations. Deputy Defense Minister Anatoly Antonov said in a video statement that if the U.S. officials indeed had the proof the plane shot down by a missile launched from the rebel-held territory, "how come they have not been made public?"

Pro-Russian rebels and Ukrainian government troops have been fighting for more than three months, leaving at least 400 dead and displacing tens of thousands.

Ukrainian forces are trying to ride the momentum of taking the strategic city Slovyansk on July 5 which was in rebel hands for more than two months. Government forces are now closing in on Donetsk, where insurgents regrouped after leaving Slovyansk, and are trying to cut off supply routes to rebels based in the neighboring Luhansk region.

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Nataliya Vasilyeva in Moscow, Lucian Kim in Donetsk and Rod McGurk in Canberra, Australia, contributed to this report.