The United States stressed its resolve to defend allies Japan and South Korea Wednesday, as it dismissed North Korea's latest threats as "saber rattling" and "bluster."
Earlier in the day, North Korea threatened to take military action against South Korean and U.S. ships taking part in a U.S-led effort to stop ships from transporting material used in nuclear bombs.
South Korea joined the U.S.-led Proliferation Security initiative after North Korea successfully conducted a nuclear test Monday.
The North Korean military also said Pyongyang will no longer be bound by the armistice that ended the Korean War.
White House spokesman Robert Gibbs said threats will not get North Korea what it wants, and suggested that Pyongyang instead focus on fulfilling its international obligations.
U.S. Secretary of State Hillary Clinton said Wednesday there will be consequences of what she called North Korea's "provocative and belligerent" behavior.
And United Nations diplomats said key powers on the U.N. Security Council are committed to broadening sanctions against North Korea.
The diplomats told reporters Wednesday the five permanent members of the council, the U.S., Britain, France, China and Russia, plus Japan and South Korea are considering travel and financial sanctions, a broader arms embargo, tougher inspections of cargo, and a freeze on North Korean assets abroad.
The U.N. officials said the Security Council plans to meet either Thursday or Friday of this week to discuss further sanctions. The council condemned North Korea's nuclear test Monday, calling it a violation of international law.
Also Wednesday, Russia's Foreign Ministry said it summoned North Korea's ambassador to express concern about the test and call on Pyongyang to return to six-nation denuclearization talks.
The U.S. State Department would not confirm South Korean media reports about additional North Korean missile tests on Wednesday, as well as reported moves to restart the country's nuclear processing facility at Yongbyon.
South Korea's Yonhap news agency has reported that North Korea fired five short-range missiles off its eastern coast on Monday and Tuesday.
A U.S. arms control institute in Washington said Wednesday commercial satellite imagery did not show steam coming from the Yongbyon facility, despite South Korean media reports.
Pyongyang began dismantling the Yongbyon facility in 2007 as part of a deal reached through the six-nation disarmament talks. But it vowed to restart the facility last month after the U.N. Security Council condemned the North's test-firing of a long-range missile.
Some information for this report was provided by AFP, AP and Reuters.