South Korea wants to work closely with the United States to force a change in North Korea's behavior so as to curb its nuclear and missile development, a senior South Korean official said Wednesday.

Cho Tae-yong, deputy chief of the presidential office of national security, made the remark upon arriving in Washington for talks with U.S. Deputy Secretary of State Tony Blinken, underlining Seoul's push for greater pressure on Pyongyang.

"The No. 1 goal of the Korea-U.S. collaboration should be on curbing North Korea's nuclear and missile development by forcing the North to change," Cho told reporters, adding that his talks with U.S. officials would be a meaningful opportunity to discuss strategies.

Cho also said that discussions aimed at putting together a U.N. Security Council resolution imposing sanctions on North Korea are going well as China shares a broad strategic goal with Seoul and Washington that the North's fourth nuclear test is unacceptable at all.

"Consultations are proceeding well with the goal that a U.N. Security Council sanctions resolution should be much stronger than previous resolutions," Cho said.

Cho also said that a decision on whether to deploy the U.S. THAAD missile defense system to the South are up to defense authorities in Seoul and Washington.

A senior South Korean official also said later in the day that differences are being narrowed down in U.N. Security Council negotiations to adopt a North Korea sanctions resolution.

The official also said that the U.S. is focusing its efforts on coming up with a meaningful U.N. resolution, and is expected to impose bilateral sanctions on Pyongyang later.

"This is a matter of sequence," the official said on condition of anonymity in response to a question why the U.S. isn't taking unilateral sanctions on the North. "I believe there will be a lot of opportunities for the U.S. to take meaningful measures." (Yonhap)