U.S. officials believe Iran accidentally shot down a Ukrainian airline and killed all the 176 people on board, U.S. media reported on Thursday.

Multiple media sources quoted unidentified officials saying they are increasingly confident that the aircraft was mistakenly downed by Iranian air defense systems based on satellite, radar and electronic data.

According to Press TV, Iran’s civil aviation authorities called the media reports “illogical rumors.”

Read More: Over 170 killed after passenger plane crashes in Tehran

The Iranian Civil Aviation Organization said Ukraine International Airlines Flight PS752 dropped just minutes after the takeoff from Tehran airport, with no pilot radio message signaling distress.

Ukraine has already sent 45 accident investigators to Tehran to assist in the Iranian authorities’ investigation.

They arrived Thursday in the Iranian capital to further examine the Boeing plane’s black box files, Ukrainian President Volodymyr Zelensky said.

Iran said it would not hand over the black boxes to the manufacturer of the US aircraft.