Samsung Electronics revealed on Monday that its first reported battery explosion case in China was due to external heating, assuring its clients in the world's biggest smartphone market that the units sold there are safe.

"The test results show that the damage to the device was caused by external heating," Samsung said in a statement.

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The investigation came after photos of charred Galaxy Note 7 from two Chinese owners went viral online. Of the two devices, only one was obtained for investigation.

In an interview with The Associated Press, one of the phone users said the handset began heating up and vibrating late Saturday night, and then it exploded, emitting black smoke. The second complaint claimed that the phone exploded on Sunday while the user was playing a game.

Amperex Technology, Samsung's battery supplier for handsets in China, said that a joint investigation with Samsung revealed that the case was not directly linked to the battery it produced.

"According to the burn marks on the sample, we surmise that the source of the heating comes from outside the battery, and it's very likely that there was an external factor causing the heating problem," Amperex said.

The two devices that exploded were bought at JD.com after Samsung officially launched the unit in China on Sept. 1, The Wall Street Journal reported. The Note 7 phones recalled in China by Samsung last week were those distributed before the official Sept. 1 launch.  

An insider told Reuters that Samsung SDI is the maker of the faulty batteries that were recalled.

Meanwhile, it is not clear whether Samsung's official statement is enough to ease worries. The company has been hit by crisis after it announced a global recall of its Galaxy Note 7 following 92 reports of Note 7 batteries overheating or catching fire in the United States, CNBC reported.

TagsSamsung, Galaxy Note 7, Samsung Galaxy Note 7 China, phone recall, china