Samsung believes that faulty lithium-ion batteries had caused its Galaxy Note7 handsets to overheat and catch fire. It came to the conclusion after tests on thousands of devices ruled out any defect in its hardware or software, company officials said at a press conference on Monday. Both in-house and independent investigations had reached the came conclusion, The Guardian reported.

“Our investigation examined every aspect of the Galaxy Note7, including hardware and software, and related processes such as assembly, quality assurance testing and logistics,” Samsung said, adding that some 700 engineers and researchers carried out tests on more than 20,000 Note7 handsets and over three lakh batteries.

The original batteries had short-circuited and led to the phones catching fire because their casing was too small, whereas a manufacturing defect had led to the same result with the replacement batteries. Multiple reports of such incidents had forced Samsung to recall 2.5 million Note7 devices in September and subsequently suspend production.

“We are taking responsibility for our failure to ultimately identify and verify the issues arising out of battery design and manufacturing,” the South Koran conglomerate said in a statement. “We have taken several corrective actions to ensure this never happens again.”

Speaking to reporters in Seoul, the head of Samsung’s mobile business, Koh Dong-jin, assured customers that its new devices will come with no fire risks, including the S8 that is expected to be launched soon. “We sincerely apologise for the discomfort and concern we have caused to our customers,” Koh Dong-jin said.