Fighting between Ukrainian troops and separatists has caused a team of international inspectors to give up plans to visit the crash site of MH17 for the day.
The setback came hours after Malaysia announced it had agreed with Ukrainian rebels to allow international police personnel to enter the crash site.
Alexander Hug, deputy head for the Organization for Security and Cooperation in Europe's (OSCE) monitoring mission in Ukraine, told reporters in Donetsk that "we heard indications there's fighting going on."
He added, "The situation on the ground appears to be unsafe...we therefore decided to deploy tomorrow morning."
He was flanked by Dutch and Australian experts.
Earlier, Dutch and Austrialian experts including policemen were reported to be en route to the crash site following a new agreement between the OSCE and separatist leaders.
Malaysian Prime Minister Najib Razak's office said July 27 police would be allowed to enter the area in eastern Ukraine "to provide protection for international crash investigators."
The agreement was reached with separatist leader Aleksandr Borodai.
Malaysia was earlier able to persuade Borodai to turn over the black boxes of flight MH17.
The head of the Dutch crash investigation mission in Ukraine, Jan Tuinder, told reporters on July 26 in Kharkiv that the Dutch government was sending policemen to Kharkiv.
"This police mission is to be set up to get the last human remains and personal belongings -- which are left behind in the place where the disaster took place, at the crash zone -- to bring these remains and these belongings back home," Tuinder said.
The Dutch are in charge of victim identification and leading the probe into what caused the crash.
Australia is sending a total of 190 police and 40 troops to the Netherlands to participate over the coming days in the Dutch-led operation to secure the crash site.
Australian officials said July 27 "a number" of armed personnel will enter the MH17 crash site in separatist-controlled eastern Ukraine next week, but stressed they would be a "nonthreatening force" unaccompanied by military troops.
Foreign Minister Julie Bishop said some of the Australian team at the site would carry weapons to protect investigators.
Malaysian Airlines Flight 17 was shot down over a part of eastern Ukraine controlled by pro-Russian separatists last week, killing nearly 298 people on board. U.S., U.K., and Ukrainian officials say it was shot down by a missile from rebel territory, most likely by mistake.
A truce has been called in the immediate area around the site by both Kyiv forces and the separatists, but combat has been raging just 60 kilometers away, with loud explosions heard at regular intervals in western and northern suburbs of rebel stronghold Donetsk.