Iran says it's confident that some kind of mechanical failure brought down a Ukrainian passenger jet near Tehran this week. Ukraine, however, isn't so sure. Its investigators are looking into the possibility that a missile or perhaps an explosion inside the jet as part of a terrorist attack might be responsible, reports the Wall Street Journal. "Too many things are unclear at the moment," said a Ukraine security official, cautioning that no conclusions have been reached. The crew of the Boeing 737 made no distress call before the crash and was turning back toward the airport in Tehran when the plane went down, according to an initial Iranian investigation, per the AP.
Eyewitnesses say they saw the plane on fire in the air before hearing an explosion, reports the Washington Post. All 176 people aboard were killed. "Rumors about the incident being a terrorist attack, explosion, or shooting at the plane ... are not true," said Iran's minister of roads and urban development, Mohammad Eslami. But a Ukrainian official, Oleksiy Danylov, said he wants investigators to search for remnants of a Russian missile, per Reuters. It's not clear which nation will receive the plane's black boxes. (In 2014, a missile brought down a commercial jet over Ukraine, and pro-Russian separatists were blamed.)