SEOUL, South Korea -- North Korean leader Kim Jong-un has ordered his country's nuclear weapons made ready for use at a moment's notice, the official state news agency reported Friday.

Kim also said his country will ready its military so it is prepared to carry out pre-emptive attacks, calling the current situation very precarious, according to KCNA.

North Korea has threatened nuclear war in the past, but it is unclear just how advanced the country's nuclear program really is. Pyongyang is thought to have a handful of crude atomic bombs, but there is considerable outside debate about whether it is technologically able to shrink a warhead and mount it on a missile.

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"The only way for defending the sovereignty of our nation and its right to existence under the present extreme situation is to bolster up nuclear force both in quality and quantity," the North's dispatch Friday said, paraphrasing Kim Jong Un. It said that Kim stressed "the need to get the nuclear warheads deployed for national defense always on standby so as to be fired any moment."

The U.S. does not believe that North Korea has the ability to launch its nuclear weapons, CBS News foreign affairs correspondent Margaret Brennan reported.

Annual military exercises between the U.S. and South Korea are scheduled to begin next week, with 8,600 U.S. forces in the area and 290,000 South Korean troops, Brennan said, adding that this type of saber-rattling from the North typically takes place right before the exercises begin.

South Korean army soldiers ride a K-1 tank during the annual exercise in Yeoncheon, near the border with North Korea, Thursday, March 3, 2016. Ahn Young-joon, AP

China's President Xi Jinping is also set to visit Washington later this month for a nuclear summit with President Obama.

On Thursday, North Korea fired six short-range projectiles into the sea off its east coast, South Korean officials said, just hours after the U.N. Security Council approved the toughest sanctions on the North in two decades for its recent nuclear test and long-range rocket launch.

The firings also came shortly after South Korea's National Assembly passed its first legislation on human rights in North Korea.

The North Korean projectiles, fired from the eastern coastal town of Wonsan, flew about 60 to 90 miles before landing in the sea, South Korea's Joint Chiefs of Staff said in a statement.

It wasn't immediately known exactly what North Korea fired, and the projectiles could be missiles, artillery or rockets, South Korea's Defense Ministry said.

North Korea routinely test-fires missiles and rockets, but often conducts weapons launches when angered at international condemnation.

Thursday's firings were seen as a "low-level" response to the U.N. sanctions, with North Korea unlikely to launch any major provocation until its landmark ruling Workers' Party convention in May, according to Yang Moo-jin, a professor at the University of North Korean Studies in Seoul.

North Korea has not issued an official reaction to the new U.N. sanctions. But citizens in its capital, Pyongyang, interviewed by The Associated Press said Thursday they believe their country can fight off any sanctions.

"No kind of sanctions will ever work on us, because we've lived under U.S. sanctions for more than half a century," said Pyongyang resident Song Hyo Il. "And in the future, we're going to build a powerful and prosperous country here, relying on our own development."

North Korean state media earlier warned that the imposition of new sanctions would be a "grave provocation" that shows "extreme" U.S. hostility against the country. It said the sanctions would not result in the country's collapse or prevent it from launching more rockets.

The U.N. sanctions include mandatory inspections of cargo leaving and entering North Korea by land, sea or air; a ban on all sales or transfers of small arms and light weapons to the North; and the expulsion of North Korean diplomats who engage in "illicit activities."

In Beijing, Foreign Ministry spokesman Hong Lei said China, North Korea's closest ally, hoped the U.N. sanctions would be implemented "comprehensively and seriously," while harm to ordinary North Korean citizens would be avoided.

At the United Nations, Russia's ambassador, Vitaly Churkin, asked about the North's firing of short-range projectiles, said, "It means that they're not drawing the proper conclusions yet."

Japan's U.N. ambassador, Motohide Yoshikawa, said, "That's their way of reacting to what we have decided."

"They may do something more," Yoshikawa said. "So we will see."

In January, North Korea conducted its fourth nuclear test, which it claimed was a hydrogen bomb. Last month, it put a satellite into orbit with a long-range rocket that the United Nations and others saw as a cover for a test of banned ballistic missile technology.

Just before the U.N. sanctions were unanimously adopted, South Korea's National Assembly passed a bill that would establish a center tasked with collecting, archiving and publishing information about human rights in North Korea. It is required to transfer that information to the Justice Ministry, a step parliamentary officials say would provide legal grounds to punish rights violators in North Korea when the two Koreas eventually reunify.

North Korea, which views any criticism of its rights situation as part of a U.S.-led plot to overthrow its government, had warned that enactment of the law would result in "miserable ruin."

In 2014, a U.N. commission of inquiry on North Korea published a report laying out abuses such as a harsh system of political prison camps holding up to 120,000 people. The commission urged the Security Council to refer North Korea to the International Criminal Court over its human rights record.