U.S., U.N. Slap Back at North Korea After Nuclear Threat

Do you know who you're messing with?

The Obama administration warned of "costly consequences" for North Korea on Thursday, in the wake of Pyongyang's threat to launch a pre-emptive nuclear strike on the US and its recent nuclear test.

Speaking at a Senate hearing, the US State Department's special representative on North Korea said Washington would not engage in negotiations without a "fundamental change in attitude" from the pariah state.

The Senate foreign affairs committee chairman, Robert Menendez, described the threat of a nuclear strike as "absurd and suicidal".

The hearing was taking place as the United Nations security council voted in New York to expand sanctions against North Korea. The US-drafted resolution was approved unanimously by the 15-nation council. It came after three weeks of negotiations between the US and China after North Korea's latest nuclear test on 12 February.