Speaking to reporters in Seoul, visiting U.S. Deputy Secretary of State William Burns also assured of his country's continued support for South Korea's defense and security, Yonhap News Agency reported.
"I think the United States and our friends here share a lot of concerns about the recent behavior of the [North Korean] leadership, and the dangers of further reckless behavior and provocations in the future," Burns said.
North Korea, an isolated Communist country led by its unpredictable leader Kim Jong Un, executed Kim's once powerful uncle Jang Song Thaek last month, accusing him of treason. Later, Kim was quoted as saying in an address that the "purge of anti-party and counterrevolutionary factionalists has strengthened the party" and without naming him, called Jang "factional filth."
South Korea already is concerned the North may resort to military provocations as part of its strategy to forge internal unity in the wake of Jang's execution.
Last week, analysts warned the North may resort to provocative acts because of its opposition to the joint military drills by South Korea and the United States starting next month. The North wants the drills canceled despite assurances they are routine and defensive in nature.
The North already is under tightened sanctions by the United Nations for conducting missile tests and its third nuclear test a year ago.
Burns spoke to reporters after meeting with South Korean Vice Foreign Minister Kim Kyou-hyun.
The U.S. official vowed continued cooperation with South Korea "in dealing with challenges posed by the North Korean leadership," expressing "strong American support for [South Korean] President Park's principled approach" to North Korea, and to South Korea's defense and security, Yonhap said.
On the stalled talks on North Korea's nuclear weapons program, Burns said the United States and South Korea "remain committed to the resumption of credible and authentic negotiations aimed at denuclearization." Other countries in the talks are China, North Korea, Russia and Japan.
The talks have been stalled since late 2008. South Korea and the United States have insisted the talks cannot resume unless North Korea demonstrates its sincerity to denuclearize through actions.
Burns' next stop on his tour is China.