MONTREAL (Reuters) - Investigators from the U.N. aviation agency have arrived in Ukraine to help probe the crash of a Malaysian airliner but cannot reach the site because of safety concerns, a senior agency source said on Sunday.
The Montreal-based International Civil Aviation Organization (ICAO) is taking part in the effort to determine what happened to the airliner, which was shot down by a missile on Thursday over eastern Ukraine.
Pro-Russian rebels in the area and Ukrainian authorities blame each other for the disaster, in which 298 people died.
A senior ICAO official told Reuters that safety concerns meant the two investigators who were in Ukraine could not reach the crash site or examine the plane's flight recorders.
"Nobody has been allowed to have access to the site for that purpose," said the official, who was not authorized to speak to the media.
"Until safe passage for them is assured we don't send people into that kind of situation."
The official said the four-person team would be free from the political influence of the U.N. agency's 191 member states.
It is unusual for ICAO to take a direct role in an investigation, and the team's assignment comes in response to a request from Ukraine's government.
The head of Emirates, one of the world's largest airlines, on Sunday called for an international meeting of carriers to see what changes needed to be made in the way the industry tackles regional instability.
In the wake of the crash, ICAO denied it had either opened or closed the route the Malaysian plane took over eastern Ukraine when it was shut down.
Malaysian officials said ICAO had approved the route - a responsibility the agency does not have. ICAO also said "it is not our job" to warn carriers about the dangers of missiles.
Kenneth Quinn, a partner at the Pillsbury law firm in Washington and a former chief counsel at the U.S. Federal Aviation Administration, said the Ukrainian-led probe could have a tough task given signs that evidence had been moved.
The ICAO team's main task is to secure the site and retrieve information from the flight data recorders. It would also review air traffic control tapes, study radar tracking, obtain satellite imagery, and set up forensic and specialist teams, Quinn said in an email.
"Given the apparent circumstances, metallurgy will be particularly important to see missile signatures and fragmentation of the fuselage," Quinn said.
One crucial area of the overall probe would be run by law enforcement teams from agencies such as Interpol and the U.S. Federal Bureau of Investigation, who would look for evidence that could lead to a criminal prosecution, he added.
"This is a particular challenge for all investigators, as it would appear the scene has been significantly compromised. Security of course is also a problem since the plane went down in rebel-controlled areas," he said.
(Additional reporting by Tim Hepher in Paris; Writing by David Ljunggren; Editing by Paul Simao)