North Korea has vowed to launch a pre-emptive nuclear strike against the United States, amplifying its threatening rhetoric hours before athe UN security council voted to impose new sanctions on Pyongyang for a recent nuclear test.

An unidentified spokesman for Pyongyang's foreign ministry said the North will exercise its right for "pre-emptive nuclear strikes on the headquarters of the aggressors" because Washington is pushing to start a nuclear war against it.

Although North Korea boasts of nuclear bombs and pre-emptive strikes, it is not thought to have mastered the ability to produce a warhead small enough to put on a missile capable of reaching the US. It is believed to have enough nuclear fuel, however, for a handful of cruder devices.

Such inflammatory rhetoric is common from North Korea, but it has been coming regularly in recent days. The Pyongyang regime is angry over the possible sanctions and over upcoming US-South Korean military drills.

At the UN in New York, the US-drafted resolution was approved unanimously by the 15-nation security council. It came after three weeks of negotiations between the US and China after North Korea's latest nuclear test on 12 February.

The UN secretary general, Ban Ki-moon, a former South Korean foreign minister, said the resolution "sent an unequivocal message to [North Korea] that the international community will not tolerate its pursuit of nuclear weapons."

The resolution specifies some luxury items that North Korea's elite will not be allowed to import, such as yachts, racing cars, luxury automobiles and certain types of jewelry. This is to close a loophole that previously allowed countries to decide for themselves what constitutes a luxury good.

The export of luxury goods, and items related to Pyongyang's nuclear and missile programs, to North Korea has been prohibited since 2006, though diplomats and analysts say the enforcement of UN sanctions has been uneven.

Susan Rice, the US ambassador to the United Nations, said: "The strength, breadth and severity of these sanctions will raise the cost to North Korea of its illicit nuclear program and further constrain its ability to finance and source materials and technology for its ballistic missile, conventional and nuclear weapons program,

"When North Korea tries to move money to pay for its nuclear and ballistic missile programs, countries must now block those transfers even if the money is being carried in suitcases full of bulk cash," she said.

China's ambassador Li Baodong reiterated Beijing's calls for a resumption of the stalled six-party aid-for-disarmament talks between the two Koreas, United States, China, Russia and Japan. "We want to see full implementation of the resolution. The top priority now is to defuse the tension, bring down heat, focus on the diplomatic track."