Speaking at news conference in Kyiv on Saturday, Vitaly Naida, said Russian citizens were directly involved in bringing down the passenger airliner with a missile, resulting in the death of all 298 people on board.

"We have compelling evidence that this terrorist act was committed with the help of the Russian Federation," the intelligence chief said, as quoted by Reuters. "We know clearly that the crew of this system were Russian citizens."

Crash site integrity 'compromised'

Ukraine has also accused pro-Russian separatists in eastern Ukraine near the crash site of interfering with the investigation by removing victims' bodies and parts of the airplane. It has also made accusations that the rebels were destroying evidence.

There were similar concerns voiced from Malaysia: "the integrity of the site has been compromised, and there are indications that vital evidence has not been preserved in place," said Malaysian Transport Minister Liow Tiong Lai at a press conference Saturday in Kuala Lumpur.

The Reuters news agency has reported that separatist leader Aleksander Borodai said the rebels have not touched the bodies but are concerned about them remaining exposed to the heat.

Reports also indicate observers from the Organization for Security and Cooperation in Europe (OSCE) trying to view the crash site on Saturday were not being given full access by the rebels, which have control over the crash site.

Merkel pushes for ceasefire

German Chancellor Angela Merkel had a telephone conversation with Russian President Vladimir Putin on Saturday, where both agreed that a rapid ceasefire between Ukrainian military forces and the separatists was necessary to ensure an independent international investigation into the crash could be carried out.

"Both agreed that an international, independent commission under the leadership of the International Civil Aviation Organization (ICAO) should get quick access to the crash site of the Malaysia Airlines passenger plane in east Ukraine," a statement from Merkel's deputy spokesman, Georg Streiter, read on Saturday.

Streiter also indicated that Merkel urged Putin to use his influence with the rebels to help bring about peace.

mz/hc (dpa, Reuters, AFP, AP)