SEOUL, South Korea — South Korea’s military on Friday released a video that it said showed a North Korean missile abnormally spiraling early in flight and exploding, a rare publicizing of surveillance footage to dismiss the North’s claim of a successful test.

Footage filmed by a thermal observation device with South Korean frontline units showed a projectile spiraling out of control on an irregular flight path, then disintegrating.

The South Korean military assessed that “instability during flight” led to the missile’s explosion, it said in a statement on Friday, calling North Korea’s claims of success “deception and exaggeration to cover up the failure.”

North Korean state media had said that Pyongyang successfully conducted an important test on Wednesday aimed at developing missiles able to deploy multiple warheads, a claim rejected by South Korea.

North Korea’s missile administration used the first-stage engine of a solid-fuel intermediate-range ballistic missile to test separation and guidance of multiple warheads, according to the North’s official KCNA news agency.

South Korea’s military said it had detected signs of missile launch preparations early on Wednesday and was watching as the rocket was launched.

In April, Pyongyang said it had tested a new solid-fuel hypersonic missile with intermediate range, part of an intensifying race for the next generation of long-range rockets hard to track and intercept.