(CNN) -- The families of two U.S. journalists detained in North Korea made public pleas for their release, as their trial and the threat of years in labor camps loom.

The women, Laura Ling and Euna Lee, are to go on trial Thursday on spying charges.

"Our families have been quiet because the situation is very sensitive, and we've been really trying to allow diplomacy to take its course," Lisa Ling, Laura's sister, said on CNN's "Larry King Live" on Monday night. "But you know, you'd have to be hiding under a rock not to see what's going on in the Korean Peninsula.

"I mean tensions are so heated," she continued, "and the girls are essentially in the midst of this nuclear standoff."

Late last month, North Korea conducted nuclear and missile tests, drawing the condemnation of the U.N. Security Council.

"We just felt like it was time for us to talk publicly and try and encourage our two governments to try to communicate, to try and bring our situation to a resolution on humanitarian grounds -- to separate the issues," said Ling, who is a special correspondent with CNN.

Laura Ling and Lee are reporters for California-based Current TV, the media venture of former U.S. Vice President Al Gore.

The pair was reporting on the plight of North Korean defectors living along the border of China and North Korea when they were taken into custody on March 17.

North Korea said the reporters had entered the country illegally. The women were accused of "hostile acts" and charged with spying.

Until now, their families had not commented publicly, citing the sensitive nature of the case.

Contact with the women has been extremely limited.

The Swedish ambassador to North Korea was allowed to see the two journalists Monday, according to the U.S. State Department. Sweden represents the United States in North Korea because the two countries, which fought on opposite sides during the three-year Korean war in the 1950s, do not have diplomatic relations.

The ambassador also met separately with the two journalists on March 30 and May 15.

Despite the limited communication, the families say they've heard enough to know the women are "terrified" and "extremely scared."

"While I am trying to remain hopeful, each day becomes harder and harder to bear," Ling wrote in the letter that her husband, Iain Clayton, read on "Larry King Live." "I am so lonely and scared. But baby, thinking of you gives me strength. You know I can feel you here with me." Watch Lisa Ling and other family members discuss the journalists' detention »

The mounting movement to free the women is reminiscent of the one waged for Roxana Saberi, an American journalist released by Iran last month after originally being sentenced to eight years in prison for espionage.

Lisa Ling made a direct on-air appeal to North Korea in an effort to win the release of her sister and Lee.

"We don't know the details of what happened on March 17th, but if at any point the girls went into North Korea, then we apologize on their behalf," Ling said. "They never intended to do so."

"We beg your government to allow (them) to come home."

All About North Korea • Laura Ling • Euna Lee • Roxana Saberi