New details are emerging about Wednesday's plane crash in Iran as investigators hunt for clues as to what brought down a Ukrainian-operated Boeing 737 minutes after takeoff in Tehran, killing all 176 people on board. A Ukrainian official said Thursday that multiple potential causes for the crash of Ukraine International Airlines flight PS752 were being investigated, including terrorism, a missile strike, or catastrophic engine failure. The development came as an initial report by the Iranian Civil Aviation said the jetliner was on fire before it crashed. The Iranian report, citing witnesses, said the plane also changed directions after a problem and turned back toward the airport. Ukraine's National Security and Defence council chief, Oleksiy Danilov, wrote on Facebook that a meeting was taking place Thursday with Iranian authorities, where various causes behind the crash were "being studied," including a theory that the plane was hit by an anti-aircraft missile. Other theories under consideration are whether there were technical problems with one of the plane's engines that caused it to explode, whether the plane could have collided with a drone or "other flying object," or whether an technical problems with the plane's engine that caused it to explode, or whether there was an explosion inside the plane. Conflicting claims about potential causes for the disaster began hours after the crash, when Iranian state media blamed technical issues for the crash and Ukraine ruled out rocket attacks. Within hours on Wednesday, officials in both countries had walked back those initial statements. Ukraine International Airlines (UIA) defended its record on Wednesday, saying that given the level of the flight crew's experience, it was highly unlikely the crash was the result of error. This is the carrier's first crash. UIA was founded in 1992, a year after Ukraine's independence from Moscow. Tehran's airport is complicated and the pilots required several years of training to use it, said UIA President Yevhenii Dykhne. The captain had 11,600 hours of flying on a Boeing 737 aircraft while the pilot had 12,000 hours on the aircraft. The crash came hours after Iran fired missiles at two Iraqi bases housing US troops in retaliation for the killing of its general, leading to speculation over the timing of the incident.