North Korea's military Monday threatened "special actions" soon to turn parts of the South Korean capital to ashes, accusing Seoul's conservative government of defaming its leadership.

The North has for months been criticizing the South's President Lee Myung-Bak in extreme terms and threatening "sacred war" over perceived insults.

North Korea has been developing a new long-range ballistic missile in a separate program from the one that led to a failed rocket launch this week, a South Korean TV station reported Saturday.

YTN quoted an intelligence source as saying the communist state carried out four tests over 16 weeks until early this year to develop an inter-continental missile at a test facility at Musudan-ri on the northeastern coast.

North Korea announced Friday it would launch a rocket carrying a satellite next month, just 16 days after agreeing to suspend long-range missile tests in return for massive U.S. food aid.

The United States, Japan, and South Korea condemned the plan and said it would breach a United Nations ban imposed after previous launches.

North Korea's new leaders, hungry for food aid ahead of a landmark anniversary, have bought time in a deal with Washington but show no sign of actually renouncing their nuclear bargaining chip, experts say.

Under the deal announced Wednesday, the communist state now led by the young and untested Kim Jong-Un agreed to suspend nuclear and long-range missile tests, and its uranium enrichment program.

South Korea staged live-fire drills Thursday from a front-line island shelled by North Korea in 2010, the first such exercise since North Korean leader Kim Jong Il died last month.

Marines at Yeonpyeong Island and nearby Baengnyeong Island fired artillery into waters near the disputed sea border during the two-hour-long drills, a South Korean Defense Ministry official said. The drills were routine exercises and there haven't been any suspicious activities by North Korea's military, the official said on condition of anonymity, citing department rules.

South Korea's president opened the door Monday to possible nuclear talks with North Korea and warned the neighboring country to avoid any provocations, saying the Korean peninsula is at a crucial turning point.

Lee Myung-bak's comments in a nationally televised speech come as the young son of the late Kim Jong Il takes power in North Korea as Supreme Commander of the military and ruling party leader after Kim's death last month. The North vowed Sunday in a New Year's message that it would bolster its military and defend the son, Kim Jong Un, "unto death."

North Korea warned the world Friday to expect no policy changes under new leader Kim Jong-Un, and threatened retaliation against South Korea for "rubbing salt" into the wounds of its grieving people.

The tough statement came a day after the communist nation ended 13 days of mourning for late leader Kim Jong-Il, and proclaimed his son Jong-Un as new supreme chief at a massive memorial ceremony.

A former South Korean first lady and a leading businesswoman crossed the border to North Korea Monday to pay respects to its late leader Kim Jong-Il.

Lee Hee-Ho, 89, widow of late president Kim Dae-Jung, and Hyundai Group chairwoman Hyun Jung-Eun, 56, will also meet officials during their two-day trip.

Minutes after the announcement of North Korean leader Kim Jong-Il’s death, the world leaders were on alert on Monday urging Pyongyang to engage with the global community.

The United States swiftly closed ranks with its ally South Korea, as President Barack Obama called his close friend President Lee Myung-Bak of South Korea at midnight on the U.S. east coast, as Washington and its regional allies digested the death of the Stalinist state's volatile 69-year-old leader.

The United States was Sunday "closely monitoring" reports on North Korean leader Kim Jong-Il's death and said it was committed to stability on the Korean peninsula and the security of its allies.

Kim's death, announced by North Korea's official media, posed an immediate and grave foreign policy crisis for Washington and its allies, given Pyongyang's history of belligerence and its nuclear arsenal.