South Korea’s military said Tuesday that it believes North Korea is being deceptive in claiming to have launched a new intermediate-range ballistic missile(IRBM) tipped with a hypersonic warhead.

The assessment from the Joint Chiefs of Staff(JCS) came hours after Pyongyang said it successfully test-fired the IRBM the previous day, claiming the missile flew some 15-hundred meters at Mach 12, or 12 times the speed of sound.

According to JCS spokesperson Col. Lee Sung-jun during a regular briefing, the military believes the stated flight distance and second peak altitude are “highly likely deception.”

The spokesperson said the flight range analyzed by Seoul, Washington and Tokyo was eleven-hundred kilometers and that the warhead did not reach a second peak, dismissing Pyongyang’s claim that it peaked again at 42-point-five kilometers.

When asked whether the North could have received technological assistance from Russia in developing the latest missile, Lee said he could not rule out the possibility.

The question about Russia arose after North Korea claimed on Tuesday that the missile reflected technological advancements, such as the use of new carbon fiber composite materials in the missile’s engine.

Previously, in April, North Korea launched an IRBM tipped with a hypersonic warhead and called it a “powerful, strategic offensive weapon” while claiming it had traveled one-thousand kilometers.

At the time, the JCS said that missile flew only 600 kilometers and accused the North of exaggerating, but said the regime appeared to have made some technological advancements to its hypersonic weapons program.