The announcement comes as Clinton and Secretary of Defense Robert Gates visited South Korea, part of a rare meeting with members of the key Asian ally.

The new sanctions, which will include freezing of some assets, are also aimed at barring North Korea from purchasing and selling arms

The high-level U.S. delegation arrived in Seoul this week to show support for South Korea over the sinking of its war ship.

The warship, called Cheonan, sank in March. A multinational investigation found North Korea responsible for the torpedo attack that killed 46 South Korean sailors.

North Korea has denied any connection and said it is the victim of an international conspiracy.

Gates and Clinton toured the infamous and heavily armed Demilitarized Zone (DMZ) dividing the two countries since the 1953 armistice between the communist North and democratic South.

Both pledged support for South Korea while sending strong messages to the North.

Gates said South Korea has improved since the last time he was there 20 years ago.

"The North, by contrast, stagnates in isolation and deprivation. And as we saw with the sinking of the Cheonan, it continues its history of unpredictable and at times provocative behavior," Gates said.

Clinton also added a verbal jab.

"The Republic of Korea has made extraordinary progress. It has leaders who care about the well-being of the people. By contrast, the North has not only stagnated in isolation, but the people of the North have suffered for so many years," she said.

Gates and Clinton also held their first meeting with their South Korean counterparts in Seoul to discuss numerous diplomatic and military issues concerning North Korea.