The U.S. State Department spokesman Robert Wood said Secretary of State Hillary Clinton had been in touch with representatives of the four other permanent five nations and would make more calls on Monday.
"We're going to continue to go forward in discussions with our partners in the council to see and to seek a strong, coordinated and effective response," Wood said.
Susan Rice, in her CNN interview, said, "We believe the most appropriate form for that response to take would be a Security Council resolution with some teeth in it.
"We will continue to work in that direction, but we have also to look at our bilateral mechanisms and further steps." The goal, she said, is "a nuclear-free Korean Peninsula."