South Korea has held an emergency national security meeting following news that North Korea has executed the uncle of leader Kim Jong Un, who until recently was seen as one of Kim's chief advisers.
Seoul says it is watching the events with concern and will work closely on the issue with allies and related governments.
The North's official news agency says Jang Song Thaek was put to death Thursday after facing a special military tribunal.
The United States said it could not immediately verify Jang's execution, but had no reason to doubt it. White House spokesman Jay Carney said the execution was another example of the "extreme brutality" of the North Korean regime, but declined to speculate on the motivations behind it.
"What it is indicative of, however, is the values of the regime, their low regard for human life, and what is probably the worst human rights record in the world, and that's saying something."
Mitchell Reiss, president of Washington College and former director of policy planning at the U.S. State Department, says he thinks Jang's relationship with Kim Jong Un was overrated by many outside of North Korea.
"I think that his role as an adviser and guide to the young Kim was probably overstated from the beginning based on wishful thinking, particularly by the Chinese."
China has reacted to the news by saying it is North Korea's internal affair.
Lawrence Korb, a senior fellow at the Center for American Progress and a former assistant secretary of defense, says the execution could force China to recalculate its relations with Pyongyang.
"I think it is much more an internal struggle and says very little about South Korea or China. In many ways I think it will move China to be much more cautious in whatever aid or help they give them because they're not quite sure what this young ruler will do."
China's ties with North Korea have been strained since North Korea conducted an underground nuclear test earlier this year. But Beijing remains Pyongyang's most important ally.
(This report was produced in collaboration with the VOA Korean service.)