Photo: The Canadian Press. All rights reserved.

An Ukrainian government army military vehicle travels across a damaged bridge near the village of Debaltseve, Donetsk region, eastern Ukraine, Thursday, July 31, 2014. (AP Photo/Dmitry Lovetsky)

With the sound of artillery fire in the distance, dozens of international investigators arrived Friday at the zone where a Malaysia Airlines plane crashed in eastern Ukraine and began preparations to comb the rural area for remains of as many as 80 victims and jet debris.

Several hours before they arrived, at least 10 Ukrainian soldiers were killed when their convoy was ambushed by pro-Russian separatist rebels in a town close to the wreckage site. Thirteen more soldiers were unaccounted for after the attack, officials said, and the bodies of four more people were being examined to determine whether they were soldiers or rebels.

The investigators from the Netherlands and Australia plus officials with the Organization for Security and Cooperation in Europe travelled from the rebel-held city of Donetsk in 15 cars and a bus to the crash site outside the village of Hrabove. Then they started setting up a base to work from at a chicken farm.

As the investigators prepared equipment for the search, an Associated Press reporter heard the artillery fire.

The investigative team's top priority is to recover human remains that have been rotting in midsummer heat of 90 degrees (32 degrees Celsius) since the plane went down on July 17. They will also try to retrieve the belongings of the 298 people killed who were aboard the Boeing 777.

Ukraine and the West contend the plane was shot down by the rebels with a Russian-supplied missile. Rebel leaders publicly deny it, but one top rebel official has told the AP on condition of anonymity that insurgents were involved in the operation that downed the plane.

Friday's search effort came after a smaller advance investigative team managed to perform a preliminary survey of the area a day earlier. For days, clashes along routes to the wreckage site had kept investigators from reaching the site. Independent observers warned that there has been tampering with evidence.

The sprawling site of fields in between two villages will now be officially designated a crime scene and divided into grids that will be systematically searched for remains, victims' belongings and jet crash evidence, Australian police officer Brian McDonald told reporters in Hrabove. Specially trained dogs will be also be used in the search.