The United States is pursuing "every possible channel" to secure the release of two American journalists imprisoned in North Korea, Secretary of State Hillary Clinton said Monday, expressing deep concerns about the secrecy of their trial and the severity of their sentences. 

TV reporters Laura Ling and Euna Lee were found guilty of a "grave crime" against North Korea and of illegally crossing into the country, and were sentenced to 12 years in labor prison. 

Clinton said the United States seeks their release on "humanitarian grounds" and that North Korea should immediately grant the prisoners clemency and deport them. 

"Obviously we are deeply concerned about the length of the sentences and the fact that this trial was conducted totally in secret," Clinton said. "We're engaged in all possible ways through every possible channel to secure their release." 

With the sentence, the likelihood seemed to increase that the prisoners would be used as pawns in the ongoing standoff between North Korea and its neighbors and the West. 

Clinton said international concern over North Korea's nuclear ambitions should be "entirely separate" from the trial. 

White House Press Secretary Robert Gibbs said Monday that the administration is working for the journalists' release, and that it hopes the North Koreans do not link their detainment to "other issues." 

"These women are innocent and should be released to their family," Gibbs said. 

But South Korean sources told FOX News the prisoners are expected to remain in North Korea for at least several months, if not longer, while North Korea uses them to its political advantage. 

They said it would take a "good will gesture" or some signal toward "normalization" from the United States to make any progress toward their release. 

The swift and harsh sentencing could change the landscape in efforts to censure and punish the rogue regime for its nuclear test last month and its series of short-range missile tests. The fact that the United States is pushing for a strong United Nations Security Council resolution against the regime does not bode well for the journalists' early release. 

On Sunday, Clinton also said the United States was willing to consider re-designating North Korea a state sponsor of terrorism -- the country was taken off the State Department's list in October 2008. And Clinton said the administration is working with allies to develop ways to cut off North Korean shipments that may be carrying nuclear technology. 

But New Mexico Gov. Bill Richardson, the former U.N. ambassador who helped negotiate the release of Americans from North Korea in the 1990s, said the situation is now a "high-stakes poker game" and "political negotiations" must begin. 

Richardson told NBC's "Today Show" that "diplomacy and negotiation for the humanitarian release" can start now that the legal process has ended. 

"In previous instances where I was involved in negotiated releases, you couldn't even start until the legal process had ended," he said. Though the sentence was harsh, Richardson said the good news is the journalists were not charged with espionage. 

Richardson said the administration, which has reached out to him for advice, would probably seek a political pardon or something similar. 

Administration officials said shortly after the sentence came down that they were working toward the release of the prisoners. 

"The president is deeply concerned by the reported sentencing of the two American citizen journalists by North Korean authorities, and we are engaged through all possible channels to secure their release," White House spokesman Bill Burton said. 

The threat posed by North Korea's rogue behavior, though, does not appear to be diminishing. 

The country has warned fishermen and boat captains to stay away from the country's east cost, Japan's coast guard said Monday, in another sign that the regime is planning to fire medium-range missiles in that area as expected. 

President Obama said Saturday that he prefers diplomacy in dealing with Pyongyang's missile tests but, "We are not intending to continue a policy of rewarding provocation." 

As for the imprisoned journalists, sources said they probably will not be exposed to harsh prison camp conditions -- such treatment would lead to concerns they would "tell all" about horrendous conditions if they are released. 

They are now believed to be held in "guest houses" in Pyongyang. 

The journalists work for Current TV, the media company led by former Vice President Al Gore. It's unclear what role Gore could play in securing the journalists' release. 

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