The Joint Chiefs of Staff(JCS) said on Monday that North Korea's recent claims on its nuclear-capable underwater attack drone might have been exaggerated or fabricated.

North Korea's official Korean Central News Agency on Friday reported that the regime conducted a test of a new underwater nuclear attack drone from Tuesday to Thursday under the guidance of leader Kim Jong-un. The report added that the test results verified the reliability and safety of the drone and proved its lethal strike capability.

In a message to reporters on Monday, the JCS said that based on the analysis of South Korean and American and experts' opinions, the military is weighing the possibility that the North's claim was exaggerated and fabricated.

The JCS said there have been signs that North Korea is developing an unmanned submarine, but it seems to be still in the early stage, adding that South Korea will closely monitor the development. 

The JCS stressed that the Seoul-Washington alliance maintains a firm combined defense posture while keeping a close eye on various threats from North Korea, including the weapons systems related to the unmanned submarine.