North Korea early on Thursday fired two short-range missiles travelling a distance of 430km (270 miles) and reaching an altitude of 50km before falling into the Sea of Japan, also known as the East Sea.
It comes after anger from the North over planned military exercises between South Korea and the US next month.
The North warned they could affect the resumption of denuclearisation talks.
The first missile was launched at about 05:34 Thursday local time (20:34 GMT Wednesday) and the second at 05:57, said the JCS.
They were launched near the eastern city of Wonsan. It is not clear if North Korean leader Kim Jong-un oversaw this launch.
North Korea arms control expert Jeffrey Lewis said in a tweet that the missile “looked like a pair of KN-23s”.
According to Mr Lewis of the Middlebury Institute of International Studies, KN-23s are capable of delivering a “nuclear-weapon sized payload… far enough to target most US forces in South Korea”.
South Korea’s defence ministry has urged Pyongyang to stop acts that it said were unhelpful for easing tension, reported Reuters.
Read more: Reuters