Monitors said on July 22 that they had seen uniformed men cutting into the cockpit section of the fuselage with a power tool. Since then, the cockpit has been further dismantled, Mr. Bociurkiw said. If the earlier work might have been justified by a search for bodies after the plane was shot down on July 17, he said, it was unclear why metal-cutting tools were still being used. “The cockpit slammed into the ground and pancaked and now it’s opened up,” he said. “It was quite stunning.”

Monitors also said they saw body fragments elsewhere in the debris field on Friday.

Ukraine has ceded control of the inquiry into the downing of Flight 17 to the Netherlands, the nation with the largest number of citizens on board, and the Dutch government has pressed to secure the site as well as the safety of an investigative team still waiting in Kiev for access. The Dutch prime minister, Mark Rutte, said his government intended to send 40 unarmed border police officers. The Australian government is also pressing to deploy the police to protect the site.

On Friday, the militia at the site apparently rejected this suggestion. Mr. Bociurkiw said the armed men controlling the area wanted no more than 35 investigators.

The separatists also indicated that they intended to gather the debris and ship it out of the war zone by train, Mr. Bociurkiw said during a nightly briefing in Donetsk, and that they could begin doing so within days. He added that the militia leadership argued that the wreckage cannot be secured against looting as it was, scattered in and around villages. The separatists suggested sending the pieces to Kharkiv, a city in Ukrainian-controlled territory that also became the destination for a trainload of victims’ bodies, as a transfer site for onward shipment to the Netherlands.