"We have a new set of sanctions measures coming forward as we speak," Sullivan said on Wednesday during an event hosted by the Center for Strategic and International Studies.
The Biden adviser told eventgoers that North Korea has completely rejected sincere US efforts to engage in dialogue to resolve bilateral issues over Pyongyang's nuclear weapons program.
"Pyongyang has today completely rejected this sincere outreach," Sullivan said on Wednesday during an event hosted by the Center for Strategic and International Studies. "In the event that they [North Korea] chose to take a different tack and to engage, we're prepared to explore practical steps that would increase regional security and address the interests of both sides."
Sullivan's remarks come as North Korea has conducted dozens of missile test launches since the start of 2022, firing several missiles at once on some occasions.
Earlier in November, North Korea launched more than 20 short-range missiles. Pyongyang said its missile tests were in response to "provocations" by the US and its regional allies, South Korea and Japan.
The Japan Air Self-Defense Force (JASDF) conducted a missile interceptor drill near a nuclear plant on the Sea of Japan coast in Fukui prefecture on Monday, amid concerns over North Korea's recent test launches.