Laura Ling and Euna Lee, reporters for former Vice President Al Gore's California-based Current TV, were arrested March 17 near the North Korean border while on a reporting trip to China.
North Korea's official Korean Central News Agency said in a brief dispatch earlier Thursday that the trial would begin at 3 p.m. (0600 GMT; 2 a.m. EDT) in Pyongyang's Central Court. Hours later, there was no word on the status of the proceedings.
U.S. State Department spokesman Robert Wood said Thursday that American officials had seen news reports that the trial had begun but had no independent confirmation. The North has told United States that no observers, including Swedish officials who act as the U.S. protecting power in Pyongyang, would be allowed to watch the trial, he said.
The trial began at a time of mounting tensions on the Korean peninsula following the regime's provocative May 25 nuclear test.
With discussions continuing at the United Nations and in Washington on how to punish the regime for its defiance, there were fears the women could become political pawns in the standoff with Pyongyang.
Analyst Choi Eun-suk, a professor of North Korean law at Kyungnam University, said the court could convict the women and then the government could use them as bargaining chips in negotiations with the U.S.
"The North is likely to release and deport them to the U.S. -- if negotiations with the U.S. go well," Choi said.
North Korea and the U.S., former Korean War foes, do not have diplomatic relations, and analysts called Pyongyang's recent belligerence a bid to grab President Barack Obama's attention.
Pyongyang "believes the Obama administration has not made North Korea a priority," said David Straub of Stanford University's Korean studies program.
Back home, the reporters' families pleaded for clemency.
"All we can do is hope the North Korean government will show leniency," Ling's sister, TV journalist Lisa Ling, said in an emotional plea at a California vigil Wednesday night. "If at any point they committed a transgression, then our families are deeply, deeply sorry. We know the girls are sorry as well."
She urged Washington and Pyongyang not to let politics dictate the reporters' fate.
"Tensions are so heated, and the girls are essentially in the midst of this nuclear standoff," she said on CNN's "Larry King Live." She urged the governments to "try to communicate, to try and bring our situation to a resolution on humanitarian grounds -- to separate the issues."
State-run media have not defined the exact charges against them, but South Korean legal experts said conviction for "hostility" or espionage could mean five to 10 years in a labor camp. Choi said a ruling by the top court would be final.
The circumstances of their arrest were hazy. The Current TV team had gone to the Chinese border city of Yanji to report on the trafficking of North Korean women, Lisa Ling said.
"Too many sad stories," her younger sister posted to Twitter days before her arrest.
They were seized somewhere near the frozen Tumen River dividing North Korea and China while a cameraman and their guide managed to evade the North Korean guards.
For weeks, there was little word about their condition in separate quarters in one of the world's most isolated nations. Sweden's ambassador to North Korea has visited the women and brought back a letter from Laura Ling saying she "cried so much" at first but was passing the time doing daily stretches and meditating.
Lisa Ling said she got a surprise phone call last Tuesday from her "extremely scared" younger sister, asking for help.
"My sister said that the only hope that she and Euna had to get released was if our government and North Korea's communicated directly," Lisa Ling said. "'I know that you've been trying to get other countries involved,' she said, 'but our only hope is if our countries talk."'
The State Department has not divulged details about the sensitive negotiations for their freedom.
"We continue to consult with the families. And there is no higher priority that we have than protection of American civilians abroad," spokesman P.J. Crowley said Wednesday in Washington.
"And we, again, hope that North Korea will forgo this legal process and return them to the United States."
Twice in the 1990s, New Mexico Gov. Bill Richardson, then a congressman, was sent as a special envoy to negotiate the release of Americans detained by North Korea.
In New York, dozens turned out in a drenching rain for a vigil led by Ling's cousin Angie Wang. Some held yellow chrysanthemums.
"Nobody should be holding people for purely political gamesmanship purposes," said J.B. Miller, 44.
Media groups also pressed for their release.
"We urge that their fate not be linked to the ongoing security situation on the Korean peninsula," Bob Dietz of the Committee to Protect Journalists said in a statement. "Euna Lee and Laura Ling were acting as journalists, not criminals, and should be released."
Roxana Saberi, an American journalist who spent four months in an Iranian prison before being freed May 11 on a suspended sentence for spying, urged the women to "remain strong."
"If Laura and Euna's situation resembles anything like mine, I can imagine a little of what they might be wishing for: The presumption of innocence until proven guilty. A fair trial, with access to attorneys of their choice and the right to study what is claimed as evidence against them. More contact with their families, whom they probably worry are worrying about themselves!"