Nuclear-armed North Korea test-fired a short-range missile off its east coast on Monday, the same day it announced the death of leader Kim Jong-Il, South Korea's Yonhap news agency said.

The agency quoted an unnamed government official as saying the missile launch was unrelated to the announcement that Kim had died Saturday of a heart attack.

The young man tipped to be North Korea's next leader and propel the Kim dynasty into a third generation is even more of an enigma than his mercurial father Kim Jong-Il, who has died at the age of 69.

North Korean state media on Monday urged people to pledge allegiance to Kim's youngest son and heir apparent Kim Jong-Un, aged in his late 20s, after the stunning announcement that his father had died on Saturday.

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.

North Korean leader Kim Jong-Il has died aged 69 of a heart attack, state media announced Monday, plunging the impoverished but nuclear-armed nation into uncertainty amid a second dynastic succession.

The official Korean Central News Agency (KCNA) said the leader "passed away from a great mental and physical strain" at 8:30 am on Saturday (23:30 GMT Friday), while on a train for one of his "field guidance" tours.

North Korea has agreed to suspend its enriched-uranium nuclear weapons program, a key United States demand for the resumption of disarmament talks, news reports said Saturday.

Yonhap news agency and the Chosun Ilbo daily quoted an unidentified diplomatic source saying the Washington had also agreed to provide the North with up to 240,000 tons of food aid.

South Korea said Monday it would display Christmas lights near the tense border with communist North Korea despite Pyongyang's threats to retaliate against what it calls psychological warfare.

The defense ministry will allow Seoul church groups to string up the lights on three tree-shaped steel towers atop military-controlled hills near the border, a ministry spokesman told Agence France Presse.

South Korea is reportedly pushing for U.S. permission to recycle spent nuclear fuel for power generation as the two countries resumed talks to revise a 1974 pact on the use of atomic energy.

The focus of the three-day talks until Thursday will be the peaceful use of nuclear energy, including Seoul's right to reprocess spent fuel, Yonhap news agency said.

U.S. Secretary of State Hillary Clinton won promises of further reforms from Myanmar's rulers in historic talks Thursday, but said it was too soon to end sanctions after decades of repression.

Paying the most senior U.S. visit in more than half a century to a nation long distrustful of the West, Clinton offered only cautious incentives to encourage more action, despite a call by China for Western sanctions to be lifted.

South Korea's defense chief said Thursday that North Korea may use provocations next year to deal with economic woes and political instability stemming from a second dynastic succession.

Defense Minister Kim Kwan-Jin described 2012 as a critical year for security saying the military should stay alert against any provocations by North Korea.