HRABOVE, Ukraine (AP) — A team of several dozen international investigators descended Friday on the Malaysia Airlines Flight 17 crash site in eastern Ukraine to begin combing an area now designated as a crime scene.

A few hours earlier, 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. Defense officials said another 13 servicemen remained unaccounted for after the attack.

Investigators from the Netherlands and Australia, along with accompanying officials from the Organization for Security and Cooperation in Europe, traveled in 15 cars and one bus to the crash site, outside the village of Hrabove.

By midday, they began setting up base at a chicken farm for an operation that will initially focus on recovering several dozen bodies still remaining. As the expert team prepared equipment for the search operation, rounds of artillery could be heard periodically falling somewhere in the distance.

In addition to tracking down human remains, the team aims to retrieve the belongings of the 298 people killed when the Boeing 777 was shot down last month.

A small advance team managed to perform an initial survey of the area for the first time Thursday. For days, clashes along routes to the wreckage site had kept investigators from reaching the area to find and retrieve bodies that have been decaying in the 90-degree (32 C) midsummer heat. Independent observers warned that there has been tampering with evidence.

An Australian police official told reporters Friday that the wreckage would be officially designated a crime scene and that it would be divided into zones that will be systematically searched for evidence.

It is believed up to 80 bodies may still remain uncollected at the crash site, which is sprawled in a broad area across fields between two villages.

The team's drive to the area took them from their base in the rebel capital of Donetsk, through the government-held town of Debaltseve, and back into the separatist-controlled territory, where the wreckage lies. At Debaltseve, the convoy was joined by three vehicles from the International Committee of the Red Cross.

Despite both sides in the ongoing conflict in east Ukraine tentatively agreeing to a cease-fire around the crash zone, fighting is continuing nearby.

The deadly attack by rebels on government troops Friday morning took place less than 20 kilometers (12 miles) south of the crash site, outside the town of Shakhtarsk, which has been the object of sustained battles for several days and still remains in rebel hands.

Defense officials said in a statement that an army convoy was struck by mortars during redeployment.

Ukraine security spokesman Vladislav Seleznev said the attack took place at 6 a.m., before the end of the 24-hour "day of quiet" declared Thursday in response to a call for a cease-fire from U.N. Secretary General Ban Ki-moon.

"The militants are behaving in a cowardly and shameless fashion," Seleznev said. "The used the 'day of quiet' just to fire on us."

Another Ukraine defense spokesman, Andriy Lysenko, said another 13 soldiers have been reported missing in action after the attack.

Seleznev said the bodies of another four people killed in the incident have not yet been identified.

Ukrainian forces have latterly focused their strategy on driving a wedge into an area between the largest rebel-controlled cities, Donetsk and Luhansk. Shakhtarsk lies on one of two highways linking those cities.

In Donetsk, meanwhile, one person was killed Friday and three others were wounded when mortar fire struck a minibus carrying passengers near the central train station was struck by mortar fire, city hall spokesman Maxim Rovensky.

The city government in Luhansk said five residents were killed and nine wounded as a result of shelling over the past day.

Neither of the city halls specified who they believe was responsible for the shelling.

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Leonard reported from Kiev, Ukraine. Associated Press reporter Yuras Karmanau contributed to this report from Donetsk, Ukraine.