Forensics investigators conducted their first day of work at the crash site of Malaysia Airlines Flight 17 on Friday, combing the ground for victims' belongings and remains that have languished for two weeks as battles raged between Ukraine's government and pro-Russia rebels.

Ukraine said it had lost at least 10 of its troops in an ambush by separatists not far from the site and claimed shelling continued to come from across the border with Russia, an allegation its neighbor has denied.

The development came the day after investigators managed to reach the site for the first time in nearly a week as Ukrainian forces observed a one-day cease-fire. The Kiev government has been rapidly advancing in its fight against the separatists controlling parts of the east, but the violence has hindered investigators' progress.

"The first step has been made," Dutch Prime Minister Mark Rutte said. The safety situation remained very unpredictable, he said, and the decision to go to the crash site will be taken daily based on constant monitoring.

President Barack Obama on Friday spoke with Russian President Vladimir Putin, the White House and the Kremlin said. It was the first phone call between the two leaders since they spoke on July 17, the day Flight 17 was shot down.