You've seen their faces – the two American journalists captured and accused of spying in North Korea. Today, they are set to go on trial. The sister of one of the journalists, reporter Lisa Ling has pleaded for their release. CNN's Jason Carroll reports on what a trial in North Korea could mean.

The top-ranking U.S. military officer said Monday that North Korea's reported nuclear test is a primarily a diplomatic matter right now, not a military one.

"I think it's really important ... right now to emphasize the diplomatic path," Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, told CNN's "American Morning."

"Obviously we've got forces deployed to that part of the world, we have had for a significant period of time, we've got over 25,000 troops who are stationed in South Korea," he added. "We've got very close alliances there with Japan and South Korea as well. ... The countries who are involved in [the six-party talks], I think, are absolutely critical as we move forward to address this increasingly belligerent challenge from North Korea."

Mullen said the test did not come as a surprise to the United States.

"We weren't surprised because of recent statements by North Korean leadership that they intended to do this," he said.

"As you know, they also recently ... unsuccessfully launched potentially an intercontinental ballistic missile."

He said the reported test shows Pyongyang is becoming "increasingly belligerent."

[cnn-photo-caption image=http://i2.cdn.turner.com/cnn/2009/images/05/25/intv.walsh.art.jpg caption="International security analyst Jim Walsh speaks to CNN's Kiran Chetry about the North Korean nuclear threat."]

North Korea delivered on its threat Monday, conducting a second nuclear test that angered governments around the globe. The North had threatened to do so unless the U.N. Security Council apologized for imposing sanctions on it following a rocket test on April 5.The secretive communist state also apparently test-fired a short-range missile on Monday, the White House said.

Jim Walsh, an international security analyst at the Massachusetts Institute of Technology, says more sanctions against North Korea will not work. He spoke to Kiran Chetry on CNN’s “American Morning” Monday.

Kiran Chetry: What does this claim from North Korea about the nuclear test and short-range missiles mean?

Jim Walsh: If you're just waking up on Memorial Day and you look at the headline, you say, my gosh, North Korea has had a nuclear test does this mean war, does this mean military conflict? The answer is no… We've had a previous North Korea nuclear test. It did not result in military conflict. And I don't think that's what’s going to happen this time either. What we're really talking about are not military consequences but political consequences. Both inside North Korea, which is undergoing some sort of transition, and regionally with Japan, with China, with South Korea. So it is an unwelcome event, I have to underline that, but there's no reason for panic or fear.

Chetry: If we're trying to understand what's going on with that nation, what does North Korea want, what does North Korea want to prove with these tests?

Walsh: Well, if I could answer the question, what precisely does North Korea want, I would be a wealthy man and I’d be on an island somewhere, not in the studio right now. Because at the end of the day, we don’t know that much about North Korea. Anyone who says they're 100% sure, you know, I wouldn't trust what they say. But we can have some guesses. One theory, a popular theory for some time, is North Korea does this sort of thing in order to improve its bargaining position. By taking a provocative action, suddenly people scamper and want to do something to ratchet back the tension and it also has the effect of dividing the countries in the six-party talks. Japan tends to get quite upset about these things; China, less so.

That divides the parties, improves the country's leverage. That's the traditional theory. There are some, and I'm starting to move to from the traditional theory to this alternative notion, which is this is less driven by external events and bargaining and more by internal concerns. Again, Kim Jong-il had a stroke. There's no clear line of succession. They are now in the process of trying to establish some sort of order for a new leader in North Korea at some point and when that sort of thing happens, governments often have shows of strength and that's not unusual for North Korea in particular to do that sort of thing when there's domestic change at home.

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Former Secretary of State Madeleine Albright speaks to CNN's Carol Costello about North Korea's rocket launch.

It's been three days since North Korea ignored the demands of the U.S. and its allies with a rocket launch.

The UN Security Council still has no official response, even after two days of closed-door meetings. We've also learned that a commercial satellite, owned by digital globe, apparently captured images of Sunday's launch.

Former Secretary of State Madeleine Albright joined us live.

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What do you think? What actions should the UN Security Council take in response to North Korea's rocket launch?

U.S. Ambassador to the U.N. Susan Rice speaks to CNN's Kiran Chetry about North Korea's rocket launch.

North Korea's controversial missile launch on Sunday sent the UN Security Council into an emergency session and President Obama was woken up at 4:30am with a phone call in Prague.

It's the President's first major international security dilemma. But even after hours UN officials left their late night meeting with no response.

America's Ambassador to the United Nations, Susan Rice, joined us live.

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What do you think? What steps should the United Nations take in response to North Korea's missile launch?