The Dutch Safety Board says its preliminary report into the cause of the Malaysia Airlines Flight 17 disaster will likely not be released until sometime in September.

Flight 17 was shot down in eastern Ukraine on July 17, killing all 298 people on board, most of them Dutch. The Netherlands is leading an international investigation into the cause of the crash.

Safety Board spokesman Wim van der Weegen said Wednesday that normally under International Civil Aviation Organization rules, a preliminary report is published one month after a crash date. But in this case the difficulty in accessing the crash site amid fighting between Ukrainian forces and pro-Russian separatist rebels has pushed the timeframe back.

"It's a very complicated situation," he said.