North Korean leader Kim Jong Un has a choice ahead for his country, U.S. National Security Advisor Robert O'Brien said on Sunday: be prosperous, like South Korea — or be a pariah state.

O'Brien's comments, which also included a warning that the U.S. would be "extraordinarily disappointed" — and will "demonstrate that disappointment" — if Pyongyang tests another nuclear weapon or long-range missile, come as Washington braces for Kim Jong Un's long-awaited year-end deadline for negotiations.