Seven people were killed including four Russians when a privately-owned helicopter crashed in Istanbul after hitting a television tower on Friday, local media reported, quoting the city's mayor.
"Seven people were killed in the accident. I would like to send my condolences to the loved ones and to the companies they belonged to," Istanbul mayor Kadir Topbas said, quoted by Hurriyet daily.
Turkish media speculated that foggy weather may have caused the crash.
Two pilots and five passengers were on board the Sikorsky S-76 helicopter owned by Turkish conglomerate Eczacibasi, the private Dogan news agency said.
Bulent Eczacibasi, head of the conglomerate, said in televised comments that "four Russian guests" were on board the aircraft as well as a company executive.
The Russian ministry of foreign affairs' crisis centre confirmed on Twitter four Russian nationals were among the dead.
Turkish media images showed the helicopter in pieces and thick black smoke as rescue teams continued their search in Buyukcekmece, a western district of Istanbul.
The helicopter had taken off from the main Istanbul Ataturk airport at 11.16 am (0816 GMT) and four minutes later crashed after hitting a television tower, the Turkish transport ministry said, quoted by state-run news agency Anadolu.
No one on the ground appeared to have been injured after the crash, the Buyukcekmece district mayor Hasan Akgun said.
Istanbul has seen thick layers of fog in the past few days causing disruption to travel with flights and ferry services cancelled earlier this month.
The crash came as Turkish President Recep Tayyip Erdogan met with his Russian counterpart Vladimir Putin on Friday in Moscow.