THE HAGUE/DONETSK, Ukraine, July 28 -- Escalating conflict between government forces and insurgents in eastern Ukraine has hampered an investigation into the crash of the Malaysia Airlines Flight MH17.

The Netherlands, which lost 194 Dutch nationals in the crash, temporarily scrapped a plan to send a military mission to secure the crash site on Sunday due to security concerns.

"Obtaining a military superiority by an international mission in this area would not be realistic, is our conclusion," said Prime Minister Mark Rutte.

The Netherlands and Australia also postponed additional deployment of unarmed police to the site, a plan Australian Prime Minister Tony Abbott deemed "the safest way" to conduct the mission.

Abbott said that by using unarmed police, Ukraine's parliament would not need to ratify the deployment as it would with the armed ones.

Some 63 Dutch researchers and unarmed military police officers were operating in Ukraine's Donetsk to help recover bodies of the crash victims.

Ukraine's government troops increased assaults on territory held by insurgents on Sunday in an attempt to gain control over the area where the Flight MH17 went down.

The conflict was raging in at least five places and Donetsk region health officials said at least 13 people were killed in the fighting in the town of Horlivka.

Alexander Hug, deputy head for the Organization for Security and Cooperation in Europe (OSCE) said monitors would not visit the site on Sunday.

"The situation on the ground appears to be unsafe ... We therefore decided to deploy tomorrow morning," Hug told reporters in Donetsk. "Fighting in the area will most likely affect crash site," he said.

Ten days after the disaster, only a few international experts have been able to access the site.

Meanwhile, Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry on Sunday called for immediate ceasefire in eastern Ukraine.

"Russian and U.S. top foreign policy officials agreed that it was important to end the fight in the conflict zone immediately, and to start talks between the conflicting parties in compliance with the Geneva statement made by Russia, the U.S. and Ukraine on April 17," Russian Foreign Ministry said.

But the two sides kept blaming each other of hindering the investigation work. Both said it was the other side that contributed to the escalation of violence in eastern Ukraine.

The EU reached an agreement Friday to add further sanctions against 15 Ukrainian and Russian individuals and 18 entities which they said were deemed responsible for actions against Ukraine's territorial integrity.

Russia, in response, accused the EU of curtailing bilateral cooperation by imposing new sanction measures against it.

"The new sanction list is a direct indication that the EU countries have chosen the course toward fully phasing out interaction with Russia on international and regional security sphere," the Russian Foreign Ministry said in a statement Saturday.

In the Netherlands, where the identification work of victims was going on, a total of 227 coffins had arrived in the central city of Hilversum where forensic experts would identify the remains. The fatal crash of the Boeing 777 airliner on July 17 killed all the 298 people aboard.