The International Civil Aviation Organisation (ICAO) said it had recently warned of a safety issue in the region near where Malaysia Airlines flight MH17 crashed.
Aviation experts believe the airline may have chosen to pass across the area to “save on fuel costs”.
Flight MH17 was en route from Amsterdam to Kuala Lumpur when it was apparently blown out of the sky by a missile near Ukraine’s border with Russia.
Up to 27 Australians have died on board the Malaysia Airlines passenger jet that was shot down by a ground-to-air missile over Ukraine, killing all 298 passengers and crew.
But Malaysian prime minister Najib Razak says the aircraft’s flight route was declared safe by the ICAO .
Mr Razak says the International Air Transportation Association had stated that the airspace the aircraft was traversing was not subject to restrictions.
The Malaysia Airlines European chief executive says crossing eastern Ukraine was not unusual since the area had not been classified as a war zone for aviation purposes.
The ICAO is responsible primarily for air safety.
On April 3 it warned there was a potentially unsafe situation arising from the presence of more than one air traffic services provider.
It has released a statement saying flight MH17 crashed just outside the Simferopol Flight Information Region, which had been the subject of the earlier warning.
The organisation says it stands ready to support the accident investigation upon request and has expressed its deep regret over the loss of passengers and crew.
Meanwhile, UK aviation security expert Chris Yates has told Radio National air traffic controllers should have warned the airliner of the danger.
“The aircraft perhaps should not have been in that area at that time and that ultimately is the fault of the air traffic control authorities, who should perhaps have warned all civil aircraft [who were] operating near the zone to avoid it if at all possible,” he said.
Earlier, Qantas released a statement saying it has flown that route in the past, “but hasn’t flown it for several months”.