The Obama administration is working with U.S. allies to develop ways to cut off North Korean shipments that may be carrying nuclear technology or other weapons.
"We will do everything we can to both interdict it and prevent it and shut off their flow of money," Clinton said of possible attempts by North Korea to ship nuclear material. She spoke on ABC's "This Week."
Clinton also said the U.S. is considering returning North Korea to a list of state sponsors of terrorism, after President Barack Obama pledged "a very hard look" at tougher measures because of the North's nuclear stance.
Clinton, appearing on ABC's "This Week," called North Korea's latest actions "very provocative and belligerent." The communist regime performed a nuclear test last month and has conducted a series of short-range missile tests.
The actions have triggered condemnation from the international community, but little concrete action. Asked about a request from a group of senators for the administration to consider re-designating North Korea a terrorism sponsor, Clinton said, "Well, we're going to look at it."
"There's a process for it," she said. "Obviously we would want to see recent evidence of their support for international terrorism."
North Korea was taken off the list in October, as the regime appeared to make concessions on its nuclear program. Clinton said Sunday North Korea is undermining that agreement.
"We take it very seriously," she said. "I mean, obviously they were taken off of the list for a purpose and that purpose is being thwarted by their actions."
Clinton said she's also looking for additional sanctions against the country in the United Nations, and potentially an arms embargo or other measures. She called for a "very strong resolution with teeth that will have consequences for the North Korean regime."
The secretary of state also suggested she's concerned the trial of two American journalists in North Korea could become too intertwined with the diplomatic and political standoff between North Korea and the international community.
"Clearly, we don't want this pulled into the political issues that we have with North Korea, or the concerns that are being expressed in the United Nations Security Council," she said. "This is separate. It is a humanitarian issue and the girls should be let go."
Calling the charges "absolutely without merit or foundation," Clinton said she's been directly involved in talks over the trial and that she hopes the two young women are sent home quickly.
The Associated Press contributed to this report.