The Obama administration is particularly uncertain about how to respond to Mr. Kim, who took power from his late father, Kim Jong Il, only 16 months ago, according to administration officials.

WSJ: North Korea Warned

Some senior U.S. officials have said that the Obama administration doesn't want to take any actions that could destabilize North Korea or give Kim Jong Il reasons to unilaterally pull out of negotiations aimed at ending Pyongyang's nuclear program.

WSJ: U.S. to Allow North Korea Test Launch

Mr. Iijima was a top adviser to former Prime Minister Junichiro Koizumi, and was deeply involved in organizing his visit to North Korea for talks with then-leader Kim Jong Il in the early 2000s, which led to the release of several Japanese abductees.

WSJ: Trip to Pyongyang Irks Tokyo's Allies

China, North Korea's main backer, has not yet given its official reaction to Kim Jong-il's death.

BBC: Kim Jong-il death triggers swift regional reaction