Kim Jong-Un on a submarine
American detained for attempting to swim to North Korea to meet Kim Jong-un KCNA via Reuters

A US national has been detained by South Korean authorities while trying to swim to North Korea allegedly to meet the country's leader Kim Jong-un.

The American, thought to be of Arab descent, was arrested at about midnight by South Korean navy forces while he was attempting to swim across the Han River, which borders the North.

Seoul's marines picked him up when he was resting on the river bank reportedly due to exhaustion.

"I was trying to go to North Korea in order to meet with supreme leader Kim Jong-un," the detained American said during the grilling, reported Seoul's Yonhap news agency citing a source.

The unidentified man who is suspected to be in his late 20s or early 30s is undergoing investigation in South Korea.

"The American man was swimming northward with the current when he grew tired and laid low near the riverside. This was when he was discovered by the Marines. I believe this is the first time an American has tried to flee to the North in the Gimpo area," a security source told the Korea Herald.

The South Korean defence ministry is yet to officially release the details of the arrest.

The incident has come on the heels of North Korea sentencing American tourist Matthew Miller to six years of hard labour as he was committing "hostile acts" against the state.