North Korea warned Monday that it does not engage in "empty talk" and has "guns and bayonets" aimed at its southern neighbor, heightening tensions surrounding its threat to take military action to counter what it calls South Korean plans to invade. North Korea's military accused South Korean President Lee Myung-bak on Saturday of plotting an invasion of the North and warned of strong military steps in retaliation and "an all-out confrontational posture." South Korea denied it was planning to invade and put its military on alert. South Korea said Monday it had detected no unusual moves by the North's military, and Unification Ministry spokesman Kim Ho-nyeon said Seoul will cope with the situation in a "calm" manner. But with ties between the wartime rivals at a decade low, Lee replaced the Cabinet minister responsible for North Korean affairs with a security expert hawkish on Pyongyang, the presidential office announced Monday. Hyun In-taek advised Lee on security issues during his 2007 presidential campaign. Like the president, he is a strong critic of the "Sunshine Policy" espoused by Lee's two liberal predecessors, who sought to pave the way for reconciliation by offering the North unconditional aid. Analysts say Hyun's appointment suggests Lee will stick to his hard-line policy on the North. Tensions between the two Koreas, which technically remain at war because their 1950-53 conflict ended in a truce, not a peace treaty, have been escalating since Lee took office nearly a year ago pledging to get tough with the nuclear-armed neighbor. The North since has cut off all ties and suspended several joint projects. The North's main Rodong Sinmun newspaper renewed the country's warnings on Monday, saying it would "destroy and wipe out" invaders in "one strike" if South Korean "war maniacs ignite the fire of war." "The Lee Myung-bak group should bear in mind that our guns and bayonets... are aimed at their throats," the paper said in a commentary, carried by the official Korean Central News Agency. "We know no empty talk." Such threats are not uncommon and are typically issued through state-run media. Saturday's threats, however, were read by a uniformed army officer flanked by military flags - the first time since 1998 an officer has served as messenger rather than state media, according to South Korean officials. Despite the threats, Seoul's deputy nuclear negotiator was on a five-day visit to North Korea - the highest-level visit to the North in a year. Nuclear envoy Hwang Joon-kook and his team were expected to leave Pyongyang later Monday, officials said. The visit is seen as an indication Pyongyang has not abandoned a 2007 disarmament-for-aid pact signed by six regional powers. South Korea, the US, Japan, Russia and China promised North Korea - which tested a nuclear bomb in 2006 - aid in exchange for dismantling its atomic program, but the disarmament process has been deadlocked for months over how to verify the North's past nuclear activities. Analysts say the North's latest saber rattling also is a negotiating tactic aimed at Seoul and Washington ahead of President-elect Barack Obama's inauguration Tuesday. "North Korean wants to draw Obama's attention," said Kim Yong-hyun, a professor at Seoul's Dongguk University. He said Pyongyang wants to use the tensions with Seoul to make a case for its long-standing demand for diplomatic ties with Washington - the regime's top foreign policy goal.