The United States is using too much carrot and not enough stick to discourage North Korea's nuclear program, ex-officials and analysts said Monday after the communist nation defied international warnings with a nuclear and missile test. 

The timing of the test caught U.S. officials by surprise, though President Obama noted that recent North Korean statements previewed such a move. 

The White House rushed to respond, with Obama condemning the detonation in a written statement and then during brief remarks in the Rose Garden before heading to Memorial Day services. He called on the world to "stand up" to North Korea

But the United States was already at risk of encouraging such behavior, said analysts, who advised the Obama administration to take a firm stance against Kim Jong Il and his regime. 

"Do not go soft," said Andrew Lankov, a noted Seoul-based North Korean expert. He said for the United States to engage Pyongyang in the coming months would be to "reinforce the belief that blackmail works ... every time." 

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He was surprised that North Korea conducted a nuclear test so soon after last month's long-range missile test. "They played both cards," he said, calling Monday's actions "hysterical." 

But John Bolton, former U.S. ambassador to the United Nations under the Bush administration, warned in a Wall Street Journal column last week that a nuclear test was imminent. He wrote that North Korea has been encouraged in such "belligerence," since its 2006 test was followed by the resumption of the six-party talks -- discussions among the U.S., China, Japan, Russia and the two Koreas aimed at encouraging North Korea to give up its nuclear program. Those talks later stalled again. 

Bolton told FOX News Monday that the Obama administration should abandon the six-party talks, impose "sweeping economic sanctions" on North Korea, move to expel the country from the United Nations and return it to the list of State Sponsors of Terrorism. 

"I think we're at a moment of real testing for the Obama administration," Bolton said. "I think this incident really is that famous 3 a.m. call that the presidential candidates debated last year." 

Bolton had criticized the Obama administration for its attitude toward North Korea in recent weeks. 

Stephen Bosworth, special envoy for North Korea policy, said just two weeks ago in Japan that "everyone is feeling relatively relaxed" and "there is not a sense of crisis." Bosworth called for "patience and perseverance." He said "dialogue and negotiation" is the best course, but that the decision to conduct another test is ultimately one "that only North Korea is going to be able to make." 

Speaking on "FOX News Sunday" in March, Defense Secretary Robert Gates expressed similar resignation to what would soon be a testing of North Korea's Taepodong 2 missile. 

He said at the time there's nothing the United States could do about such a firing, though officials nevertheless warned North Korea not to go ahead with the test. North Korea fired the missile a week later. The U.N. Security Council condemned the action, and then North Korea threatened to restart its nuclear reactor. 

Gates did say economic sanctions could yield more fruit than diplomacy, an assessment with which other analysts agree. 

Stephen Yates, a fellow with the American Foreign Policy Council who previously worked under former Vice President Dick Cheney, suggested economic penalties be imposed not just on North Korea but any nation cooperating with North Korea. He said the time has come to put more pressure on China -- though China publicly condemned the North Korea test Monday. 

"It's time that we get serious," Yates said, criticizing the administration for announcing to North Korea before its missile test in April that it would probably not try to interrupt the demonstration. "The president is going to have to reverse course on the politics of missile defense." 

He said the regime proved the United States "cannot afford to wait until intelligence confirms its capability, because they can surprise us even with a test." 

Analysts warn that the North Korean problem already threatens to increase the danger posed by Iran's nuclear ambitions. Not only could North Korea be sharing information about nuclear technology with Iran, but North Korea's behavior could embolden Iran. 

Though Iran reportedly stated Monday that it has no weapons cooperation with North Korea, President Mahmoud Ahmadinejad also rejected a proposal to "freeze" nuclear work and rejected talks with world powers on the matter, according to Reuters. 

The news agency reported that the Iranian navy also sent six warships into international waters. 

The United Nations Security Council was holding a closed meeting to discuss the North Korea situation Monday afternoon. 

Obama said the tests pose a "grave threat" to international security and that the world "must take action in response." 

According to the State Department, Secretary of State Hillary Clinton spoke with the Japanese and South Korean foreign ministers Monday morning about the tests and later planned to speak with her counterparts in China and Russia. 

"Secretary Clinton is engaged in intensive diplomacy," spokesman Ian Kelly said in a statement. "In her conversations, the secretary stressed the importance of a strong, unified approach to this threat to international peace and security. She consulted with them on this afternoon's Security Council meeting, and reiterated our commitment to regional security and to our alliances."

FOX News' James Rosen, Greg Palkot and Nina Donaghy contributed to this report.