07/09/2009 AT 03:35 PM EDT
Lisa Ling received an unexpected call and got "tremendous relief" when her sister Laura – who has been detained in North Korea – was on the line Tuesday night.
"It was only the first time I have heard her voice in weeks," Ling said in an interview with KOVR in Sacramento, Calif. "That silence has been just so terrifying and deafening."
The phone call comes a month after Ling, a journalist working for Current TV, and her friend Euna Lee were sentenced to 12 years
of hard labor for "their illegal border crossing," the Korean Central News Agency reported in June.
"[Laura] said, 'We are doing okay. We're being treated well and don't worry about us. We had access to physicians,'" added Ling. "We just hope that's true."
Laura "was very specific about the message she was communicating," Ling told the local TV station. "She said, 'Look, we violated North Korean law and we need our government to help us. We're sorry about everything that happened but now we need diplomacy.' "
The women were arrested by North Korean military on the Chinese border March 17 where they were researching a story about refugees in the area.