Story highlights The lawmaker was briefed Monday

North Korea tested a nuclear weapon Sunday

Seoul, South Korea (CNN) North Korea is believed to be moving an intercontinental ballistic missile (ICBM), a South Korean lawmaker said after being briefed by the country's intelligence service.

The lawmaker told CNN Tuesday it was unclear when the movement was detected, what the direction of the projectile was and how it was being transported. He attended the briefing by South Korea's National Intelligence Service (NIS) in Seoul on Monday.

All eyes have been on North Korea following the country's sixth test of a nuclear weapon Sunday. Seismological data indicated the weapon was the most powerful ever detonated by the rogue nation, nuclear experts said.

North Korean state media claimed it detonated a hydrogen bomb, also known as a thermonuclear weapon, which could be fitted atop a long-range missile capable of striking the United States.

Weapons experts say it's almost impossible to verify if the warhead and missile could be successfully paired unless North Korea were to actually fire a nuclear-tipped ICBM.

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