TOKYO - A North Korean court sentenced two U.S. journalists to 12 years in a labor camp yesterday, as the government of Kim Jong Il continued to ratchet up tension with the United States and its neighbors - but also set the stage for high-level negotiations.

Laura Ling and Euna Lee, television reporters detained March 17 along North Korea's border with China, received harsher sentences than outsiders had expected. But experts in South Korea predicted that talks to gain their release would begin soon.

Ling, 32, and Lee, 36, were working for Current TV, a cable and Web network cofounded by former Vice President Al Gore, when they were detained by North Korean soldiers.

The State Department last week did not rule out the possibility that Gore may fly to North Korea to negotiate the reporters' release. A spokeswoman for Gore contacted by the Associated Press declined to comment.

In 1996, Bill Richardson, then a member of Congress and now governor of New Mexico, traveled to Pyongyang to negotiate the release of an American who got drunk and swam across the Yalu River into North Korea.

The man, who was charged with being a spy, was released after his parents paid a $5,000 fine.

Richardson said officials of the Obama administration had been in contact with him for his thoughts on how to proceed. Asked by CNN if he would be willing to go to Pyongyang on behalf of the administration, he replied: "If they asked for my help, of course, I'd be ready to do anything. But this is something that is very sensitive at this stage."

He said that the penalty was harsher than expected but that it was a good sign espionage was not one of the charges.

"The sentence can be seen as an indication that North Korea is now expecting a very prominent envoy to come for the negotiations over their release," said Hong Jung Wook, a lawmaker from South Korea's ruling party.

The five-day trial of Ling and Lee was held in Pyongyang's Central Court, the top court in North Korea. Outside observers were not allowed.

"The trial confirmed the grave crime they committed against the Korean nation and their illegal border crossing," the official Korean Central News Agency said. It said the court sentenced "each of them to 12 years of reform through labor."

The "grave crime" was not explained. The reporters had earlier been accused of unspecified "hostile acts."

The reporters were working on a story about North Koreans who flee the country, but the circumstances of their arrest were not clear.

The detention of the two journalists has coincided with - and become entangled in - a series of provocative acts by North Korea this spring that have angered its neighbors; its longtime allies, such as China; and much of the rest of the world.

The heavily armed, secretive state - in the throes of a succession process, as its ailing leader prepares to hand power over to his youngest son - launched a long-range missile in April, detonated a nuclear bomb in May, and renounced the truce that ended the Korean War.

Yesterday, North Korea warned fishermen and boat captains to stay away from the country's east coast, Japan's coast guard said. The North is planning to launch several medium-range missiles from the region, according to reports in the South Korean press.

The U.S. government, which last year lifted some sanctions against North Korea and delivered large amounts of food aid, has become increasingly exasperated by the North's behavior.

President Obama, who came into office saying he was prepared to have a personal meeting with Kim Jong Il, said Saturday that "we are going to take a very hard look at how we move forward on these issues."

Led by the United States and Japan, the U.N. Security Council is considering new sanctions against North Korea for exploding a nuclear device in defiance of U.N. resolutions.

If sanctions are approved, North Korea threatened yesterday that it would retaliate with "extreme" measures.

The long prison terms given to the journalists add a new complication.

"We are 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," State Department spokesman Ian Kelly said yesterday.

The verdict cannot be appealed and is final, officials in Seoul have said.

But there is a widespread expectation, at least in South Korea, that the journalists will be released when the North Korean government decides the time is right to talk again to the United States.

In the past, North Korea has released Americans who have entered the country illegally. The government also has a history of brinkmanship, turning confrontation and bluster into negotiations that reward it with food, fuel, and other concessions.

"The verdict does not mean much, since they will get released," said Andrei Lankov, an expert on North Korea who teaches at Kookmin University in Seoul. "Unfortunately, right now the North Koreans want to keep tensions high, so it will take many months and perhaps a year or more before the Pyongyang authorities will decide that it's time to make some friendly gesture to Washington."

In appearances last week on U.S. television, the families of the women broke months of silence and offered public apologies to the North Korean government for whatever acts the journalists may have committed.

Both women have been allowed to telephone their families in the United States, which is highly unusual in a state that seals away political prisoners.

The women have told their families that they have been treated "fairly."