Secretary of State Hillary Clinton announced tougher sanctions Wednesday against North Korea, including freezing some assets in an attempt to keep the Communist dictatorship from buying and selling arms.
The announcement came as Clinton and Secretary of Defense Robert Gates visited South Korea, part of a rare high-level meeting with members of the government of the key Asian ally.
The U.S. delegation arrived in Seoul this week to show support for South Korea over the sinking in March of the warship Chenonan.
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 warned that North Korea might engage in other similar "provocations."
The United States and South Korea will remain vigilant and take steps toward deterrence, such as recently announced joint naval exercises, Gates said.
On the sanctions, senior U.S. officials said the aim is to go after North Korean sources of hard currency and to cut off military cooperation with some "unsavory actors" in the Middle East.
The United States is also targeting North Korea's elite and a variety of illegal trading in which they engage. This illicit sale of cigarettes, liquor and exotic food helps provide funding for North Korea's burgeoning nuclear program, U.S. officials said.
By targeting the approximately 5,000 North Korean elites, the United States hopes to put pressure on the government, the officials said. These elites are accustomed to being pampered and living in a certain way, and increased sanctions can disrupt that lifestyle, the officials said.
The United States also aims to crack down on diplomatic privileges, which have facilitated the illegal trading.
As part of their visit, Gates and Clinton toured the heavily armed Demilitarized Zone (DMZ) dividing the two countries since the 1953 armistice that halted the Korean War.
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," she said. "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."
Gates and Clinton also met with their South Korean counterparts in Seoul to discuss numerous diplomatic and military issues concerning North Korea.
CNN's Elise Labott contributed to this report