Russian President Vladimir Putin has said that the investigation of the MH17 crash site is stalling due to constant shelling of the rebel-controlled area in eastern Ukraine by Ukrainian government forces.
Mr Putin told Malaysian Prime Minister Najib Razak that rebels were not hindering access to the site of the Malaysia Airlines crash.
298 people died in the crash in July when the aircraft came down in an area controlled by pro-Russian separatists.
"Of course the rebels are not shooting, that is done by the various military groups fighting on the side of Ukraine's official authorities," Mr Putin was quoted as saying by Russian state news agency RIA-Novosti.
"The opposite side is constantly shelling this territory and that does not permit comprehensive working at the site of the crash," Mr Putin told Mr Razak as the two met on the sidelines of the Asia-Pacific Economic Cooperation summit in Beijing.
Ukraine and the west blame Russia for supplying the separatists with the Buk surface-to-air missile that shot down the Boeing 777 plane on 17 July, while Russia and Ukrainian separatists have pointed the finger at the Ukrainian government.
Five more coffins of passengers who were on the Amsterdam-Kuala Lumpur flight were flown to the Netherlands on Saturday for identification.
Meanwhile, the United States and the European Union have expressed concern at reports of Russian military reinforcements in eastern Ukraine.
European Union's foreign policy chief Federica Mogherini said reports of military reinforcements in Ukraine's separatist areas were a "very worrying development".
She called on Russia to prevent further movement of "troops, weapons and equipment".
"The most recent reports by the OSCE Special Monitoring Mission in Ukraine about convoys in separatist held areas with substantial amounts of heavy weapons, tanks and troops without insignia moving westwards represent a very worrying development," said Ms Mogherini.
The White House warned that any separatist efforts to seize more territory would be a "blatant violation" of a ceasefire agreement.
Armoured convoys headed to the frontlines as shelling rocked separatist stronghold Donetsk and fear mounted of a return to full-scale fighting.
The shelling in Donetsk was among the fiercest combat in the city since the signing of a frequently-violated ceasefire in Minsk on 5 September.
That agreement halted all-out confrontations across most of the conflict zone, but it has failed to end constant bombardments at strategic hotspots.
A convoy of 20 military vehicles and 14 howitzer cannons without number plates or markings was seen driving through the rebel town of Makiivka in the direction of the nearby frontline around Donetsk.
"We are very concerned by intensified fighting in eastern Ukraine, as well as numerous reports ... that Russian-backed and supplied separatists are moving large convoys of heavy weapons and tanks to the front lines of the conflict," said US National Security Council spokeswoman Bernadette Meehan.
"We continue to call on all sides to strictly adhere to the ceasefire.
"Any attempt by separatist forces to seize additional territory in eastern Ukraine would be a blatant violation of the Minsk agreements."
Ms Meehan urged Russia to honour the commitments it made when signing the ceasefire agreement, including halting its military supplies to separatists and the withdrawal of all its troops and weapons from Ukraine.
"Russia must enable the restoration of Ukrainian sovereignty along the Ukrainian side of the international border, to be monitored by the OSCE, and facilitate the release of all hostages," she said, referring to the Organisation for Security and Cooperation in Europe.
"We continue to stress that adherence to the framework agreed upon in Minsk is the best chance of achieving a peaceful resolution to the conflict in eastern Ukraine."
Russia denies being involved in the fighting in the east.
The OSCE voiced concern on Saturday after its monitors witnessed unmarked columns of tanks and troop carriers moving through eastern Ukraine in territory held by pro-Russian separatists.
