Russian-backed separatists still control the 13.5-square-mile debris field. Once Ukrainian government forces are able to re-take control, Ukrainian officials say investigators will be able to safely begin their work.
On Thursday, Ukraine's Parliament will convene to ratify an agreement with Australia and the Netherlands authorizing their civilian police to secure the crash site.
Col. Andriy Lysenko, spokesman for the Ukrainian National Security and Defense Council, expects "We may regain control by the time the parliament ratifies the deal. If not, they would have to wait, as we can't endanger the lives of the experts."
Lysenko said that rebels have placed heavy artillery in and around the crash site, and mines along the roads leading to the crash site.
Ukrainian President Petro Poroshenko announced Tuesday the implementation of a unilateral cease-fire in a 20-kilometer radius of the crash site. According to the president's press service, Poroshenko "expects that the OSCE will use its influence on terrorists' ceasing fire in a 20-kilometer radius as well."
On Wednesday, OSCE monitors attempted reach the crash site but were turned away by fighting.