A team of international police officers that had been due to visit the site of the Malaysian plane disaster in eastern Ukraine cancelled the trip on Sunday after receiving reports of fighting in the area.
Alexander Hug, the deputy head of a monitoring team from the Organisation for Security and Cooperation in Europe, said it would be too dangerous for the unarmed mission to travel to the area from its current location in the rebel-held city of Donetsk.
It was not immediately clear where precisely clashes had broken out.
Malaysian Airlines Flight MH17 was shot down with a missile over a part of eastern Ukraine controlled by pro-Russian separatists last week, killing all 298 people on board.
Concerns about the integrity of the site were raised further on Saturday when an Australian couple visited the wreckage-strewn fields outside the village of Hrabove and even sat down on part of the debris.
Flights from Ukraine to the Netherlands have taken 227 coffins containing victims of the plane disaster. Officials said the exact number of people held in the coffins still needs to be determined by forensic experts in the Netherlands.