ISTANBUL - One person was killed and another injured Sunday when a mysterious blast ripped through an empty apartment in an upscale Istanbul neighbourhood, Dogan news agency reported.

The incident took place in a fifth-floor apartment in Cihangir, an elegant district on the city's European side which is home to many expats. The apartment was empty at the time.

A man selling Turkish bread on the street was crushed to death by falling debris and a taxi driver was also wounded, Dogan said.

Investigators were looking into the possibility of a gas leak, several media outlets reported.

Dogan said the apartment was rented to an employee of the Greek consulate, who is currently on holiday in western Turkey.

Turkey has been on high alert following a series of attacks linked to both militants and Kurdish militants which have caused multiple deaths and damaged tourism.

On Tuesday, 11 people were killed in an attack on a police bus in the heart of the city. Six of them were police officers. The attack was claimed by a militant Kurdish group called the Kurdistan Freedom Falcons (TAK), a radical offshoot of the banned Kurdistan Workers Party (PKK).