North Korea lashed out Tuesday at the United States and reportedly launched two more short-range missiles even as U.N. Security Council members debated possible new sanctions against the communist nation for its latest nuclear test.

North Korea test-fired two short-range missiles from the east coast city of Hamhung, according to South Korea's Yonhap news agency. South Korea's spy chief said two other missiles were launched Monday, and North Korea also warned ships to stay away from waters off its west coast through Wednesday, suggesting more test flights.

The missile launches came as leaders around the world condemned North Korea for Monday's underground nuclear test. Retaliatory options were limited, however, and no one was talking publicly about military action.

Russian defense officials said the blast was roughly as strong as the bombs dropped on the Japanese cities of Hiroshima and Nagasaki in World War II and was stronger than North Korea's first test in 2006.

In New York, U.N. diplomats said key nations were discussing a Security Council resolution that could include new sanctions against North Korea.

Ambassadors from the five permanent veto-wielding council members -- the United States, Russia, China, Britain and France -- as well as Japan and South Korea were expected to meet later Tuesday, the diplomats said, speaking on condition of anonymity because the meeting is private.

The Security Council met in emergency session Monday and condemned the nuclear test. Council members said they would follow up with a new legally binding resolution.

France's deputy U.N. ambassador Jean-Pierre Lacroix said his government wants a resolution to "include new sanctions ... because this behavior must have a cost and a price to pay."

It was too early to say what those sanctions might be and whether China and Russia, both close allies of North Korea, will go along.

In an unusual step, China strongly reproached its close ally.

Chinese Foreign Ministry spokesman Ma Zhaoxu reiterated that Beijing "resolutely opposed" the nuclear test and urged Pyongyang to return to negotiations under which it had agreed to dismantle its atomic program.

North Korea is "trying to test whether they can intimidate the international community" with its nuclear and missile activity, said Susan Rice, U.S. ambassador to the United Nations.

"But we are united, North Korea is isolated, and pressure on North Korea will increase," Rice said.

Diplomats acknowledged, however, that there were limits to the international response and that past sanctions have had only spotty results.

"No one was talking about taking military action against North Korea," John Sawers, the British ambassador to the United Nations, told the British Broadcasting Corp. "I agree that the North Koreans are recalcitrant and very difficult to hold to any agreement that they sign up to. But there is a limited range of options here."

U.N. Secretary-General Ban Ki-moon said he felt "frustrated by the lack of progress in the denuclearization process" and said North Korea's only viable option was to return to the six-party talks on disarmament and continue exchanges and cooperation with South Korea.

Ban, visiting Finland, declined to comment on sanctions.

"I leave it to the Security Council members what measures they should take," said Ban, a South Korean who once took part in international talks aimed at dismantling North Korea's nuclear program.

North Korea blamed the escalating tensions in the region on Washington, saying the U.S. was building up its forces, and defended its nuclear test as a matter of self-preservation.

An editorial in the North's main newspaper, the Rodong Sinmun, called the United States "warmongers" and said Washington's recent announcement about sending fighter planes to Japan "lay bare the sinister and dangerous scenario of the U.S. to put the Asia-Pacific region under its military control."

At the Conference on Disarmament in Geneva, An Myong Han, a diplomat from the North Korean mission, said his country "could not but take additional self-defense measures including nuclear tests and the test launch of long-range missiles in order to safeguard our national interest."

The regime marked the nuclear test with celebratory speeches Tuesday at Pyongyang's Indoor Gymnasium, with No. 2 official Kim Yong Nam and senior ruling party official Choe Tae Bok presiding.

APTN video showed military officers and others at the ceremony, with placards of anti-U.S. slogans and praise for leader Kim Jong Il's "military first" policy. Kim was not seen in the video.

The test put Beijing in a particularly difficult position. Traditional allies for decades -- Chinese troops fought on the North's side in the 1950-53 Korean War -- China is still North Korea's biggest source of food, fuel aid and diplomatic support. It does not want chaos to erupt in its neighbor, sending a flood of refugees across its land border.

China's options range from agreeing to U.N. sanctions, which it has been reluctant to do, to halting key imports to stave off the complete collapse of the North's impoverished economy. Many of North Korea's international connections -- from air transport to financial links -- are also routed through China or Chinese-controlled territories.

Xiong Zhiyong, professor of diplomacy at the China Foreign Affairs University affiliated with the Foreign Ministry, said China needed to work with the U.S. to show North Korea its behavior was unacceptable, but he conceded that "past methods to intimidate and impose sanctions have proved ineffective."

Tsinghua University scholar Sun Zhe said the test had shown Beijing it could no longer carry on as before.

"There is no need for China to maintain its past policy toward its trouble-making neighbor any longer," Sun was quoted as saying in the Global Times, a newspaper published by the ruling Communist Party.

Sun reflected widespread thinking that ultimately the U.S. and North Korea would have to work out differences on their own. "China only plays the role of a peacemaker," he said.

President Barack Obama and South Korean President Lee Myung-bak "agreed that the test was a reckless violation of international law that compels action in response," the White House said after the leaders spoke by telephone.

They also vowed to "seek and support a strong United Nations Security Council resolution with concrete measures to curtail North Korea's nuclear and missile activities."

Seoul also said it would join a maritime web of more than 90 nations that intercept ships suspected of spreading weapons of mass destruction -- a move North Korea warned would constitute an act of war.

North Korea fired at least four missiles. Yonhap, quoting an anonymous government official, said the two missiles launched Tuesday -- one ground-to-air, the other ground-to-ship -- had a range of about 80 miles. Officials would not comment on the report.

Yang Moo-jin, a professor at the University of North Korean Studies, said the missile tests appeared aimed at bolstering defense of its northeastern Musudan-ni launchpad. The North launched a rocket from Musudan-ni in April that many believe was aimed at testing long-range ballistic missile capabilities. The North claims it put a satellite into orbit.

Some experts speculated the nuclear test may suggest an attempt by Kim, 67, who might want one of his sons as a successor, to mark a spectacular scientific achievement.

Analyst Koh Yu-hwan, a professor at Seoul's Dongguk University, said the test may be an attempt to get Washington's attention so that it can hold bilateral talks to possibly win much-needed aid and prestige.

The provocations and anti-U.S. tirade come with two American journalists, Laura Ling and Euna Lee of Current TV, in North Korean custody. Accused of entering the country illegally and engaging in "hostile acts," they face trial June 4.