Samsung was facing more problems with its newest line of high-end smartphones Thursday, as technology regulators ordered further battery checks.
The South Korean electronics giant has been forced to undertake a worldwide recall of the flagship Note 7 phones due to the risk of the devices catching fire.
The Korean Agency for Technology and Standards (KATS) said Thursday that Samsung's suppliers should check the safety of each battery by X-ray, as well as Samsung carrying out its own tests.
Samsung has said that an undersized battery housing inside the phone was behind the overheating, according to US authorities. The battery manufacturer in China has denied that its batteries were to blame, and pointed to "external factors."
Sales of the phone were expected to start again in South Korea at the end of September.
KATS supported the current recall, but asked that Samsung extend the recall period - which expired on Monday - until the end of the month.
This would give customers time to choose a different phone, if they did not wish to exchange their Note 7 phone for a modified model, KATS said.
About 2.5 million phones are affected by the Note 7 recall, which began at the start of this month and may affect the success of the product in a crowded smartphone market.
US authorities recorded some 92 incidences of the phone overheating or catching fire.