North Korea vows response to U.S. submarine's visit to South Korea

The powerful sister of North Korean leader Kim Jong Un vowed Tuesday to boost the country's nuclear war capability and take other steps to protest the recent arrival of a nuclear-powered U.S. submarine in South Korea.

The powerful sister of North Korean leader Kim Jong Un vowed Tuesday to boost the country's nuclear war capability and take other steps to protest the recent arrival of a nuclear-powered U.S. submarine in South Korea.

North Korea has repeatedly vowed to expand its nuclear arsenal, but the latest threat by Kim Yo Jong came after North Korea dialed up regional tensions by unveiling a uranium-enrichment facility and testing a new ballistic missile earlier this month.

In a statement carried by state media, Kim Yo Jong said that the submarine's visit "clearly reveals the frantic military and strategic attempt of the U.S." She said North Korea's nuclear war deterrent must be bolstered "both in quality and quantity continuously and limitlessly" in response.

"The U.S. strategic assets will never find their resting place in the region of the Korean Peninsula," she said. "We will continue to inform that all the ports and military bases of the ROK are not safe places." ROK stands for the Republic of Korea, South Korea's formal name.

Her comments suggested North Korea may test-fire a missile whose range covers a South Korean site where the U.S. submarine is docked, some observers say.

South Korea's military said the USS Vermont, a nuclear-powered and fast-attack submarine, arrived at the southeastern South Korean port city of Busan on Monday to take on supplies and allow its crew to rest.

Temporary deployments of powerful U.S. military assets like aircraft carriers, nuclear-powered submarines and bombers to South Korea are not unusual, but Washington has boosted them over the last year in a show of force against North Korea's evolving nuclear threats.