The US, Britain and France overcame last-minute differences with Russia and China on a UN resolution imposing punishing sanctions on North Korea, and the Security Council was expected to approve it unanimously tonight.

South Korean officials today said they believed North Korea tested a nuclear weapon as it claimed, but determining whether the atomic explosion was successful would take a couple weeks.

South Korea today said it would “sternly respond” to North Korea’s alleged nuclear test, condemning it as a provocative act.

US government officials said a wide range of agencies were looking into claims by North Korea that it had performed its first-ever nuclear test today.