President Park Geun-hye ordered the government to strengthen the level of vigilance across the country, an official said Thursday, as North Korea has ratcheted up its threats against its southern neighbor.

The chief executive also "instructed the military to be fully prepared to aggressively cope with North Korea's reckless provocations," Kim Sung-woo, chief presidential press secretary, told reporters.

North Korea threatened to turn the presidential office into a "sea of flames and ashes" and warned Wednesday that it is militarily ready to start operations to hit major targets and "mercilessly wipe out" Park and "other South Korean warmongers."

The presidential office said North Korea's latest provocation is not only a threat against South Korea and its president but a challenge to the world at large.

Reflecting the seriousness of the threat, the country convened a session of the National Security Council (NSC) during which senior officials told the military to closely monitor the North Korean situation and get ready to retaliate against the North if provoked.

The NSC told police and other relevant organizations to take all necessary measures to tighten security.

Pyongyang has accused South Korea of staging a drill on Monday in what it claims was meant to destroy the office of North Korean leader Kim Jong-un with 16 fighter bombers carrying guided air-to-surface missiles.

South Korea has confirmed its Air Force conducted a large-scale air raid drill against a simulated key North Korean facility, though it did not give details.

North Korea views its young leader as the country's "supreme dignity" that its people must protect, even at the cost of their lives.

South Korea and the U.S. began their largest joint military drills earlier this month amid heightened tensions on the Korean Peninsula following North Korea's fourth nuclear test on Jan. 6 and long-range rocket launch on Feb. 7.

The U.N. Security Council has slapped tougher sanctions on North Korea to punish the regime for the nuclear test and long-range rocket launch.

The sanctions call for, among other things, the mandatory inspection of all cargo going into and out of the North, and a ban on the country's exports of coal and other mineral resources to cut off North Korea's access to hard currency.

Also Thursday, North Korea claimed it successfully conducted a solid-fuel rocket test. The test, if confirmed, would represent a significant technological advance of North Korea's ballistic missile capabilities.

Experts say the use of solid propellant for a rocket engine would allow North Korea to launch missiles much more quickly. (Yonhap)