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The Sikorsky S-76 model helicopter hit a TV tower in the district before crashing onto a nearby highway, according to an eyewitness who spoke to private broadcaster CNN Turk, Hurriyet Daily News reported.

The cause of the accident is unknown, Sahin said, adding that an investigation into the crash was continuing.

Read alsoRussian 'friendly fire' kills Turkish soldiers in Syria - BBCAccording to sources, the helicopter that belonged to the Eczacibasi Group was carrying Eczacibasi Vitra Russia CEO Salim Ozen and four Russian guests identified as Aleksandr Vanin, Igor Kochergin, Liudmila Churova and Elena Badraga along with Turkish pilots.

"One manager and four Russian guests were on board," Bulent Eczacibasi, head of Eczacibasi Holding, told reporters at the scene.

The helicopter took off from Ataturk Airport at 11:16 a.m. and crashed five minutes later, Dogan News Agency reported.

The helicopter was heading to the Bozuyuk district of the northwestern province of Bilecik to bring the passengers to a facility belonging to the group there.

A number of ambulances and firefighters were immediately dispatched to the scene.

The E-5 motorway was also closed to traffic after the crash.