United Nations Chief Ban Ki-moon says North Korea has closed all the "doors of communication and dialogue" with its recent missile launches.
Mr. Ban expressed deep concern about the situation after North Korea shot off seven ballistic missiles into the Sea of Japan Saturday.
He told journalists in Geneva Sunday that the launches were unhelpful for peacefully resolving concerns about Pyongyang's nuclear weapons program.
Earlier Sunday, the top U.S. military officer, Admiral Mike Mullen, said he was increasingly concerned about what he called North Korea's unpredictability and belligerence.
But U.S. Vice President Joe Biden dismissed the missile launches as almost predictable, "attention-seeking" behavior.
Biden said that he did not want to give North Korea attention.
He said the Obama administration has successfully united the countries most important to North Korea, including China and Russia, on a common path of further isolating the government in Pyongyang.
North Korea drew international condemnation and violated U.N. resolutions with its launch of ballistic missiles Saturday, the U.S. Independence Day holiday.
U.S. and South Korean officials have suggested the military activities may be related to North Korea's succession process. They say ailing leader Kim Jong Il may be trying to bolster his authority as he establishes a plan to have his youngest son, Kim Jong Un, replace him.
U.S. Vice President Biden says he thinks North Korea's latest actions reflect uncertainty within the regime.