The crew of a Ukrainian jetliner that crashed shortly after takeoff from Tehran never made a radio call for help and were trying to turn back for the airport when the plane went down, according to an initial Iranian report released Thursday on the disaster that killed 176 people. The report suggested a sudden emergency struck the Boeing 737 operated by Ukrainian International Airlines early Wednesday morning, when it went down just moments after taking off from Tehran’s international airport. Investigators from Irans Civil Aviation Organization offered no immediate explanation for the disaster, however. Eyewitnesses, including the crew of another passing flight, described seeing the plane engulfed in flames before crashing, the report said. The crash caused a massive explosion when the plane hit the ground, likely because the aircraft had been fully loaded with fuel for the flight to Kiev, Ukraine. The report also confirmed that both of the so-called “black boxes” that contain data and cockpit communications from the plane had been recovered, though they had damaged and some parts of their memory was lost. It also said that investigators have initially ruled out laser or electromagnetic interference as causing the crash. The Ukrainian airliner took off at 6:12 a.m. local time and was given permission to climb to 26,000 feet, the report said. It crashed six minutes later near the town of Sabashahr. Ukrainian President Volodymyr Zelenskiy said crash investigators from his country had arrived in Iran to assist in the probe. In a television statement, Zelenskiy asked people to refrain from speculation, conspiracy theories and hasty evaluations regarding the crash. He also declared Jan. 9 a day of national mourning.