Battery problems caused Samsung Galaxy Note 7 phones to catch fire
Problems with the design and manufacturing of batteries in Samsung's Galaxy Note 7 smartphones caused them to overheat and catch fire, the company has said.
The announcement on Monday of the company's investigation into one of its worst product fiascos comes three months after the flagship phone was discontinued.
The world's biggest smartphone maker recalled 2.5 million Note 7 phones in September after reports they were overheating and catching fire. It blamed lithium batteries from a supplier.
New Note 7s with different batteries also caught fire, so Samsung permanently dropped the premium phone in October.
It estimates the problems will cost it at least £4.3 billion through early 2017.
Samsung has taken criticism for its handling of the recall and its hasty, apparently incomplete initial investigation into what went wrong.
It said 700 researchers and engineers tested more than 200,000 devices and more than 30,000 batteries and replicated what happened with the Note 7 phones.
The world's biggest smartphone maker said it was "taking responsibility for our failure to ultimately identify and verify the issues arising out of the battery design and manufacturing process".
Samsung's mobile division president, Koh Dong-jin, ruled out any problems with other aspects of the Note 7, either in its hardware or its software.
He said Samsung would use what it learned from its investigations to improve lithium ion battery safety for the industry.