Pro-Russian separatists have promised to allow international investigators free access to the site of the crash of a Malaysian passenger plane.
All 298 people on board were killed when the plane crashed on July 17 in eastern Donetsk region where Ukrainian government troops are fighting the separatists.
Bodies and aircraft parts were strewn across a 10-square-kilometer area near the village of Rozsypne -- indicating the plane broke up before hitting the ground.
The Ukrainian military and the separatists are blaming each other for shooting down the plane with a missile.
The separatists first said the two "black boxes" recording flight data had been found, but later denied those reports.
Ukrainian Prime Minister Arseniy Yatsenyuk told journalists in Kyiv on July 18 that Ukrainian authorities had still not been allowed to get to the crash site.
The Organization for Security and Cooperation in Europe (OSCE) said it expected members of its Ukraine monitoring mission to arrive at the crash site later on July 18.
Russian President Vladimir Putin called for an immediate cease-fire and direct talks between Kyiv and the separatists in the wake of the disaster.
The UN Security Council is to hold an emergency meeting on the Malaysian plane crash later on July 18.
Both Ukrainian and Russian forces have SA-17 systems, known as Buk launchers.
Ukrainian President Petro Poroshenko on July 17 termed the downing an act of terrorism.
U.S. Vice President Joe Biden said it the jetliner appeared to have been "blown out of the sky".
Authorities in Kyiv say they intercepted and recorded two telephone calls in which pro-Russian separatists were bragging about shooting down a plane in the area on July 17 before it became apparent that a civilian passenger plane had crashed there.
World leaders have called for a thorough international investigation of the crash of the Malaysian plane that was flying from Amsterdam to Kuala Lumpur.
The White House said President Barack Obama told Dutch Prime Minister Mark Rutte the United States was ready to provide "immediate assistance" for "a prompt, full, credible, and unimpeded international investigation."
Obama and Rutte also agreed on the need for "immediate access" to the site of the crash in territory held by pro-Russia separatists.
Russian President Vladimir Putin also called for an impartial investigation.
WATCH: Former U.S. Secretary of State Hillary Clinton said European nations should take the lead in an investigation of the Malaysia Airlines plane crash in eastern Ukraine.
Your browser doesn’t support HTML5
Clinton Suspects 'Russian Insurgents' Of Downing Malaysian Plane
But an angry Australian Prime Minister Tony Abbott on July 18 lashed out at Russia for blaming Ukraine, and suggested that Moscow was trying to impede an impartial investigation.
Abbott said the idea of Moscow claiming the crash had nothing to do Russia because it happened in Ukrainian airspace "frankly does not stand up to any serious scrutiny."
Abbott said it appeared that 28 Australians on the flight were killed by Russian-backed separatists in eastern Ukraine who used Russian-supplied heavy weaponry.
Abbott said an impartial investigation required from Moscow "no prevarication, no excuses, no blame shifting, [and] no protecting of people" who are backed by Russia and may have been involved in shooting down the plane.
Russian Foreign Minister Sergei Lavrov said in an interview on July 18 with Rossia-24 TV that "with regard to the claims sounded from Kyiv, that it was almost us who did it: in fact, I have not heard any truthful statement from Kyiv in the past few months."
Lavrov also accused Kyiv of interferring with and influencing future investigations by almost immediately declaring the crash a "terrorist attack."
Separatists also recently claimed that they had acquired Buk systems. But on July 18, they were denying that they had the sophisticated systems.
Kyiv's Defense Ministry said on July 18 that the plane was out of range of its antiaircraft systems and that no missiles from its arsenal were fired on the day of the crash.
Meanwhile, authorities in Kyiv on July 18 announced they were imposing a no-fly zone over eastern Ukraine.
Malaysia Airlines said there were at least 154 Dutch, 27 Australians, 23 Malaysians, 11 Indonesians, six Britons, four Germans, four Belgians, three Phillippinos, and one Canadian aboard the Boeing 777 jet.
There were another 47 passengers whose nationalities were not immediately announced. All flight crew members were Malaysians.
Ukrainian officials say up to 181 bodies have been found so far.