The Joint Chiefs of Staff(JCS) says it found discrepancies in North Korea’s claim about test-firing two strategic cruise missiles from a submarine on Sunday.

JCS spokesperson Lee Sung-joon told reporters on Monday that the South’s military does not believe the regime’s claim is completely true.

According to the North’s official Korean Central News Agency(KCNA), it conducted an “underwater launch drill” early Sunday morning with an 8.24 Yongung submarine launching the missiles from Kyongpo Bay in the East Sea.

A military official said South Korean and U.S. military authorities are trying to determine if the North was exaggerating with such a claim, adding that Sunday’s launch appears to be the early stages of a test launch.

On the method used to test-fire the missiles, the official said authorities are looking into various possibilities, including a vertical launch and a launch using a torpedo tube.

Meanwhile, the JCS said the South Korea-U.S. combined springtime “Freedom Shield” exercise will continue on schedule even in the face of the North’s missile provocations. The drill kicked off on Monday for an eleven-day run.