The Obama administration is warily watching developments on the Korean peninsula after the death of North Korea's leader Kim Jong Il and may postpone decisions on re-engaging the reclusive country in nuclear talks and providing it with food aid, U.S. officials said Sunday.

The administration had been expected to decide on both issues this week, possibly as early as Monday, but the officials said Kim's death would likely delay the process. The officials spoke on condition of anonymity due to the sensitivity of the situation. They said the U.S. was particularly concerned about any changes that Kim's death might spark in the military postures of North and South Korea but were hopeful that calm would prevail.

The White House said it was monitoring the situation closely and remained in constant contact with allies South Korea and Japan, but it offered no substantive comment on the implications of Kim's death. President Barack Obama spoke with South Korean President Lee Myung-bak at midnight and the two leaders agreed to stay in close touch.

"The president reaffirmed the United States' strong commitment to the stability of the Korean Peninsula and the security of our close ally, the Republic of Korea," the White House said in a statement.

Obama and Secretary of State Hillary Rodham Clinton were both briefed on Kim's death, the White House and State Department said.

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South Korea's military and police were placed on a high alert after Kim's death and Lee convened an emergency national security council meeting.

Kim's death was announced by state media in a "special broadcast" from Pyongyang late Sunday. The report said Kim died of a heart ailment on a train due to a "great mental and physical strain" on Dec. 17 during a "high intensity field inspection." North Korea will hold a national mourning period until Dec. 29. Kim's funeral will be held on Dec. 28, it said.

The U.S. officials stressed that North Korea's past behavior has been notoriously erratic, making predictions about its intentions difficult. However, they said they believed there would not be significant changes in North Korean policies under Kim's son and heir apparent Kim Jong Un until at least after the mourning period ends.

Kim's death came as the Obama administration was debating whether to go ahead with a new round of nuclear disarmament talks with the North and whether to provide food aid to the country, which has been struggling with crippling food shortages.

The administration had been poised to announce a significant donation of food aid to North Korea this week, the first concrete accomplishment after months of behind-the-scenes diplomatic contacts between the two wartime enemies, according to sources close to the negotiations. And, an agreement by North Korea to suspend its controversial uranium enrichment program was expected to follow within days, the sources said.

Suspension of uranium enrichment by North Korea had been a key outstanding demand from both the U.S. and South Korea of the North, which has tested two atomic devices in the past five years. Recent food talks in Beijing yielded a breakthrough on uranium enrichment, the sources said.

The food aid announcement, which could have come as early as Monday, would have not only been welcome news for North Korea, but also pave the way for a crucial U.S.-North Korea meeting in Beijing on Thursday. That meeting in turn could lead to the resumption of nuclear disarmament talks that would also include China, Japan, Russia and South Korea.

The so-called six-party talks were last held three years ago, and resuming them would amount to a foreign policy coup for the Obama administration.

Two senior U.S. diplomats were in North Korea's lone ally China last week to discuss the issues. They were due to meet Obama's top national security aides on Monday to discuss the way forward. Those meetings will go ahead in the wake of Kim's passing but decisions will almost certainly be delayed as it is not clear if North Korean officials will be in position to handle any engagement with the outside, the U.S. officials said.