ISTANBUL, Feb 14 ― Turkish authorities today detained three suspects over the collapse of an apartment building in Istanbul that claimed the lives of 21 people, local media reported.

The suspects held over the collapse in the residential district of Kartal on the Asian side of the city were identified as project officer Suzan Cayir, technical implementation supervisor Ugur Misirlioglu and building inspector Arzu Keles Boran, the state run TRT television reported.

They are charged with "killing by negligence,” according to the NTV television. 

The eight-storey block where 43 people were registered as living crumbled last week but the cause still remains unclear.

Local officials said three storeys were illegally added ― a common practice in the country's largest metropolis of around 15 million people.

The collapse fanned criticism of a government amnesty granted last year to people accused of illegal building ― a measure announced ahead of municipal elections this March.

President Recep Tayyip Erdogan, who visited the site on Saturday, said authorities have "lessons to learn” from the incident. ― AFP