The escalation in the war of words comes after President Donald Trump tweeted Kim Jong Un "won't be around much longer."
South Korea is ready to deploy graphite bombs that can paralyse North Korea's power grid in the event of a nuclear war.
Military sources told the Yonhap news agency that the "blackout bomb" works by spreading chemically treated carbon graphite filaments over electric facilities to short-circuit and disrupt the electricity grid.
The weapons have been developed by South Korea's Agency for Defence Development, as one element of the Kill Chain pre-emptive strike program.
The program is designed to detect, identify and intercept incoming missiles in the shortest possible time.
It works with Korea's Air and Missile Defence system.
"All technologies for the development of a graphite bomb led by the ADD have been secured", a military official said.
"It is at the stage where we can build the bombs at any time".
The defence ministry has also requested next year's budget include 500 million won ($617,000) for the project but the finance ministry did not accept it, he added.
Kim Jong-un attends what was said to be the test launch of an intermediate range Hwasong-12 missile at an undisclosed location in North Korea. Photo / AP
The bomb is often referred to as a "soft bomb" since it only affects targeted electrical power systems.
It was first used by America against Iraq in the 1990-1991 Gulf War and again by NATO against Serbia in 1999.
The threat comes after South Korea has continued to look for ways to boost its defensive capabilities against North Korea and its rogue leader Kim Jong un.
Graphite bombs are not lethal to those living in surrounding areas.
Their development comes as South Korea is fastracking its "three pillars" of national defence by as much as three years.
The strategy was originally scheduled to be in place by the mid-2020s.
The news comes after Kim Jong-un has promoted his sister to a senior ruling party post, and praised the country's nuclear weapons program which has sparked international alarm.
US Air Force B-1B bombers, F-35B stealth fighter jets and South Korean F-15K fighter jets fly over the Korean Peninsula during a joint drills. Photo / AP
Kim Yo-Jong becomes an alternate member of the party's powerful politburo, the decision-making body presided over by her brother, the official KCNA news agency said.
The promotion was announced along with those for dozens of other top officials at a party meeting led by the leader.
It came as the regime faces growing global pressure to curb its weapons drive following recent nuclear and missile tests.
Tensions soared as Kim traded verbal threats with US President Donald Trump, who tweeted on Saturday that "only one thing will work" to tame the isolated nuclear-armed state.
The sister, in her late 20s, has frequently been seen accompanying her brother on his "field guidance trips" and other events and is known to have been involved in the party's propaganda operations.
Both were born to the late former ruler Kim Jong-il and his third partner, former dancer Ko Yong-Hui.
The family has ruled North Korea since its creation in 1948. The current ruler came to power after the death of his father in December 2011.
Since then he has overseen four of the country's six nuclear tests - most recently in September - while cementing his grip on power through a series of purges, including those targeting his uncle and half-brother.
North Korean soldiers carrying packs marked with the nuclear symbol turn and look towards leader Kim Jong-un during a military parade in Pyongyang. Photo / AP
The uncle, Jang Song-Thaek, was executed in 2013 for treason and the half-brother Kim Jong-Nam was killed by a toxic nerve agent in a Cold War-style assassination at a Kuala Lumpur airport in February.
Both the North's missile and nuclear weapons capabilities have made significant progress under the current Kim, despite a growing layer of UN sanctions.
Kim acknowledged the country faced with "ordeals" under a "stern" situation, but claimed that its economy had grown this year despite ever-tighter sanctions.
He described the North's atomic weapons as a "treasured sword" to protect it from aggression.
"The nuclear weapons of the DPRK (North Korea) are a precious fruition borne by its people's bloody struggle for defending the destiny and sovereignty of the country from the protracted nuclear threats of the US imperialists," Kim was quoted as saying.
