The United Nations Security Council unanimously approved Thursday a new regimen of sanctions against North Korea for its third underground nuclear test last month. Just hours earlier, the rogue state threatened for the first time to launch a pre-emptive nuclear strike against United States and South Korea.

According to New York Times, the North Korean leadership said it was responding to evidences of the allies preparing for “a nuclear war aimed to mount a pre-emptive strike” on North Korea. The American-South Korean military drills are currently underway. It threatened to turn Washington and Seoul into “a sea in flames” with “lighter and smaller nukes.”

The tougher sanction imposes penalties on banking, travel and trade. It is Security Council’s fourth against North Korean government. It contains new restrictions that will block financial transactions, limit North Korea’s reliance on bulk transfers of cash, further empower other countries to inspect North Korean cargo, and expand a blacklist of items that the country is prohibited from importing.

China helped United States draft the sanction resolution. The Chinese government had told North Korean government not to proceed with Feb. 12 underground nuclear test. The Chinese support of the sanctions angered the defiant state.

“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 programs,” the United States ambassador to the United Nations, Susan E. Rice, told reporters after the vote.

“Taken together, these sanctions will bite and bite hard,” she said. “They increase North Korea’s isolation and raise the cost to North Korea’s leaders of defying the international community. The entire world stands united in our commitment to the denuclearization of the Korean Peninsula and in our demand that North Korea comply with its international obligations.”

China’s ambassador Li Baodong told reporters that China is “committed to safeguarding peace and stability on the Korean Peninsula” and that the resolution also stressed the need for resumed talks, according to New York Times.

“This resolution is a very important step, but one step cannot make a journey” he told reporters. “We need a comprehensive strategy to bring the situation back to dialogue. We need wisdom, persistence, perseverance.”

While Li said Beijing wanted to see “full implementation” of the new sanction resolution, council diplomats said the success of the new measures will depend to a large extend on the willingness of China to enforce them more strictly than it has in the past, according to Reuters.

It is uncertain if China will move beyond the scope of the resolution, cutting off fuel shipments and commercial trade with North Korea, which helped keep the isolated country functioning.

North Korean soldiers guard the Unha-3 rocket, which failed to launch in April. Pedro Ugarte/AFP/Getty Images

North Korea characterized the sanction as part of an “act of war”. Earlier this week, it declared the 1953 armistice that stopped the Korean War null and void as of next Monday.

"Since the United States is about to ignite a nuclear war, we will be exercising our right to preemptive nuclear attack against the headquarters of the aggressor in order to protect our supreme interest," the North's foreign ministry spokesman said in a statement carried by the official KCNA news agency.

According to Reuters, it is widely believed that the North does not have the capacity for a nuclear strike against the mainland of the United States.

U.N. Secretary-General Ban Ki-moon, a former South Korean foreign minister, affirmed the council’s move. He said in a statement that the resolution “sent an unequivocal message to (North Korea) that the international community will not tolerate its pursuit of nuclear weapons.”

Washington moved quickly after the new sanctions were approved and froze the assets of three North Korean citizens who have links to Pyongyang's main arms dealer.

North Korea has held a mass military rally in Pyongyang on Thursday, in support of its recent threats. It is getting ready for a state-wide war practice of an unusual scale, South Korea’s defense ministry said earlier.

Photos filed by news agencies from the North Korean capital, Pyongyang, and published in South Korean media Thursday showed buses covered with military camouflage and university students rushing out of their classroom building in military uniforms in a military exercise.

South Korea and the United States, which are conducting annual military drills until the end of April, are watching the North’s activities that they might turn from an exercise to an actual attack, said Kim Min-seok, South Korea’s defense ministry spokesman, Reuter reported.

North Korea’s last armed aggression against the South in 2010 came unannounced, bombing South Korean island and killing two civilian. It was also accused of sinking a South Korean navy ship earlier in the year, killing 46 sailors.

According to Reuters, South Korea’s military said Wednesday that it would strike back and target its leadership if Pyongyang launched an attack.