The U.N. Security Council unanimously passed tougher sanctions against North Korea Thursday targeting the secretive nation's nuclear program hours after Pyongyang threatened a possible "preemptive nuclear attack."

"These sanctions will bite, and bite hard," U.S. Ambassador to the United Nations Susan Rice said after the vote.

China, North Korea's key ally, could have used its veto power to block the sanctions. Instead, after weeks of negotiating, it signed on to the final draft.

"China is a country of principle," China's U.N. Ambassador Li Baodong said. "We are firmly committed to safeguarding peace and stability on the Korean peninsula."

Leading up to the vote, Pyongyang ratcheted up its bellicose rhetoric.

A spokesman for the North Korean foreign ministry suggested the United States "is set to light a fuse for a nuclear war."

As a result, North Korea "will exercise the right to a preemptive nuclear attack to destroy the strongholds of the aggressors and to defend the supreme interests of the country," the country said in a statement carried by the state-run Korean Central News Agency.

Despite the strong language, analysts say North Korea is years away from having the technology necessary to mount a nuclear warhead on a missile and aim it accurately at a target. And, analysts say, North Korea is unlikely to seek a direct military conflict with the United States, preferring instead to try to gain traction through threats and the buildup of its military deterrent.

But the threat came amid increased concern over Pyongyang's dogged efforts to advance its nuclear and missile technology after a recent long-range rocket launch and underground atomic blast.

On Tuesday, North Korea said it planned to scrap the armistice that stopped the Korean War in 1953 and warned it could carry out strikes against the United States and South Korea.

Analysts: 'Boxed in' North Korea's bluster 'particularly dangerous'

The rhetoric came not only in advance of the U.N. vote, but also as military drills take place on either side of the heavily armed border that divides the two Koreas.

This week, the United States and South Korean began two months of joint exercises, known as Foal Eagle. North Korea has called the annual training exercises "an open declaration of a war," but South Korea says it notified Pyongyang that the drills "are defensive in nature."

North Korea's nuclear threat Thursday "may suggest that Pyongyang feels even more boxed in than usual," said Michael Mazza of the American Enterprise Institute.

And while a nuclear attack itself is not an immediate palpable threat, "This surge in provocative rhetoric is particularly dangerous," added Michael Auslin, also with the institute. "South Korea's new president (Park Geun Hye) can't be seen to back down in the face of the North's threats, while (new North Korean leader) Kim Jong Un may feel that his successful missile and nuclear tests give him the ability to keep pressuring Seoul. The two may wind up talking themselves into conflict."

South Korea's U.N. Ambassador Kim Sook said Thursday the new resolution "reflects the will of the international community," which "will never tolerate North Korea's repeated violations and North Korea's nuclear and ballistic missile program."

"Each violation will be met by stronger responses and measures," he added.

Will the new sanctions work?

The goal of the new sanctions is to stymie the activities of North Korean banks and cash couriers who might be funneling money to the secretive regime's nuclear and missile programs.

It will be tougher for the regime to move large sums of cash stuffed into suitcases, Rice said.