Three Bulgarians, reportedly the crew of a helicopter, died when it crashed in the region of Tikrit in Iraq on Thursday April 21.
Focus news agency quoted Bulgarian National Radio as giving the names of the three victims as Lyubomir Kostov, Georgi Naydenov and Stoyan Anchev.
"A rescue operation is being conducted at the moment by the US forces located in the region of Tikrit," the executive director of Heli Air, Mihail Mihaylov, told Focus news agency.
The relatives of the deceased had been informed, he was quoted as saying.
The helicopter was hired by SkyLink, a Canadian company that does charter flights out of Baghdad.
News agencies Reuters and Associated Press quoted the Bulgarian Foreign Ministry as saying that the six passengers on board were not believed to be Bulgarians.