Speaking to a packed press conference here Tuesday, she said the rebels were "eager to cooperate" from the first day the incident occurred near the rebel-held Ukrainian village of Grabovo.
She said her opinion was based on observation made by the Organisation for Security and Co-operation in Europe (OSCE) that the pro-Russian separatists have been "helpful.
"There was a clear statement by these experts that the rebels are doing everything within their power to secure the safety of their site.
Previously, it was reported that gunmen prevented monitors from the OSCE from observing the crime scene and some of them seemed intoxicated while others would not let the investigators to look at the wreckage of the Boeing 777.
Reports on rampant looting of the victims' personal belongings also surfaced, due to alleged lack of security in the area.
However, Vorobyeva said the rebels were helpful from day one, which eventually led to the handover of two black box data recorders of the doomed plane to the Malaysian team of investigators, Tuesday morning.
"The experts have also certified that the black boxes have not been tampered with, and experts from the Netherlands have access to the bodies which were being refrigerated," she said.
The black boxes were handed to the Malaysian officials hours after Prime Minister Datuk Seri Najib Tun Razak reached an agreement with the Ukrainian rebels for custody of the black boxes and access to the crash site.
When asked if the Russian had in any way assisted to the agreement, Vorobyeva briefly responded, "no comment".
She also stressed that the rebels have called for a ceasefire since the incident occurred, but the government of Kiev has not stopped the bombings and military operations.
"Russia has been calling for a full stop fighting and peaceful dialogue by the diplomatic means and our stand has not altered," she said.