North Korea said Friday it is ditching a nonaggression pact and all other peace agreements with South Korea, in an apparent attempt to use the threat of an armed clash to press Seoul to give up its "confrontational" stance. The communist nation also said it will no longer respect a disputed sea border with the South, raising the prospect for an armed clash along the Yellow Sea boundary - the scene of deadly skirmishes between the two navies in 1999 and 2002. South Korea said it regretted the North's latest move and warned it won't tolerate any attempt to violate the border. Analysts said Pyongyang's threats could signal it is preparing for an armed confrontation, but only as a way of ratcheting up the pressure on Seoul to get the neighbor to soften its hard-line stance - and attracting President Barack Obama's attention. "This signals that North Korea will stage a provocation" - probably near the maritime border, said Kim Yong-hyun, a North Korea expert at Seoul's Dongguk University. The isolated regime could then use the threat of an armed clash to pressure Seoul to change course with the North, said Yang Moo-jin, an expert at Seoul's University of North Korean Studies. But Kim added that any skirmish would be limited in scale and intensity because Pyongyang is aware that serious deadly clashes would irreparably harm relations with Seoul - and Obama's new administration, whose attention the North is seeking, he said. A Defense Ministry official said the military has stepped up vigilance along the land and sea borders with the North. The official, who declined to give his name citing department policy, said more guard posts have been installed along the land border, but could not offer details about what's been done on the sea border. Yonhap news agency said the navy deployed a warship near the maritime boundary and strengthened radar and other surveillance systems. The ministry official said he was checking the report. The two Koreas technically remain at war because their brutal, three-year conflict ended in a truce, not a peace treaty, in 1953. The peninsula remains divided by a heavily fortified Demilitarized Zone, with thousands of troops stationed on both sides of the border. Relations had warmed considerably over the past decade, with Seoul's liberal leadership adopting a "sunshine policy" of extending aid to the impoverished North as a way to facilitate reconciliation. But South Korea's current president, conservative Lee Myung-bak, has not committed to accords signed by his predecessors - a stance Pyongyang says proves his hostility. The regime cut off reconciliation talks soon after he took office nearly a year ago. Lee has refused to give in to the pressure, saying he will "wait" until Pyongyang agrees to return to the reconciliation talks. On Friday, the North's Committee for the Peaceful Reunification of Korea - a ruling Workers' Party organ in charge of ties with Seoul - declared all past peacekeeping accords with the South "dead," claiming Lee is escalating tensions with the regime. "The group of traitors has already reduced all the agreements reached between the North and the South in the past to dead documents," the committee said in a statement carried by the state-run Korean Central News Agency. The statement specifically mentioned a nonaggression pact that the two sides signed in late 1991 pledging not to invade each other and to seek peaceful unification. The so-called Basic Agreement has served as a basis for future peace accords, such as summit agreements signed in 2000 and 2007. It also said the maritime boundary off the divided peninsula's west coast will be "nullified." The US-led United Nations Command unilaterally drew the Yellow Sea border, also known as the Northern Limit Line or NLL, at the end of the war - but Pyongyang claims it should be redrawn farther south. "The position of our military on the NLL is firm," Defense Ministry spokesman Won Tae-jae said. "If the North violates it, we will sternly respond to that." The latest verbal attack from Pyongyang comes as both Koreas watch to see how Obama's North Korea policy takes shape. After eight years of icy relations with the Bush administration, Pyongyang hopes to have improved relations with Obama, analysts say. Obama has said he would be willing to meet with Kim Jong Il if it advances the effort to disarm the North of its nuclear capabilities. Unification Ministry spokesman Kim Ho-nyeon said the government regretted the North's move and urged the regime to defuse the tensions through dialogue. The Defense Ministry said its troops remain on alert, though there have been no unusual moves by the North's military. Earlier this month, the North's military accused the South of preparing to wage war and said it had adopted an "all-out confrontational posture" to rebuff any southern aggression. Seoul denied plotting any attack on the North. North Korea, which tested a nuclear bomb in 2006, signed a pact in 2007 with five other nations - the US, South Korea, Japan, Russia and China - agreeing to dismantle its nuclear program in exchange for aid. That process has been stalled since August, and talks in Beijing in December failed to get the process back on track.