The South Korean presidential office on Sunday said North Korea’s claims of having carried out a test of an underwater nuclear weapons system were probably overstated.

In a primary analysis on North Korea’s announcement on Friday, an official with the presidential office in Seoul said that the purported test was “likely to be exaggerated and fabricated.”

The development of an underwater nuclear-based weapons system is one of the key tasks outlined in North Korea’s five-year plan for defense expansion unveiled in January last year.

“North Korea claims to have successfully tested so-called unmanned, nuclear-capable attack drones on three different occasions last year,” the official said.

“An analysis to date indicates a high likelihood that North Korea’s claims are exaggerated and fabricated.”

The official pointed out North Korea has not released any images of the test that it says it conducted on Friday, restricting the ability to verify the authenticity of the claim.

Even if such an underwater system had been tested, it is believed to have been a “torpedo of some sort” and “highly unlikely to be a nuclear propulsion system,” the official said.

While it is unknown whether North Korea’s claims are true, the official said South Korea and the US were jointly monitoring its development of underwater weapons, including nuclear torpedoes and submarine-launched ballistic missiles.

The official added that the South Korean military is already equipped with “an overwhelming capability” to strike against the launch sites of North Korean weapons in the event of contingencies.