Lisa Ling and Laura Ling

U.S. journalists Euna Lee and Laura Ling, sister of former View co-host Lisa Ling, have been sentenced to 12 years in a labor prison by North Korea's Central Court.

The reporters, who were working for Current TV, a company co-founded by Al Gore, were convicted of a "grave crime they committed against the Korean nation and their illegal border crossing," the Korean Central News Agency said.

Claiming suspicion of "hostile acts," North Korean authorities detained Lee and Ling along the China-North Korea border on March 17. The two were on assignment reporting on the plight of North Korean refugees.

"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," U.S. State Department spokesman Ian Kelley said in a statement. "We once again urge North Korea to grant the immediate release of the two American citizen journalists on humanitarian grounds."

Secretary of State Hillary Clinton said on Sunday the charges were "baseless" and that the women should be allowed to return home. The sentencing comes amid rising tensions between the United States and North Korea, which detonated its second nuclear device in as many months on May 25.

Over the weekend, President Obama said his administration does not intend "to continue a policy of rewarding provocation" in reference to North Korea's nuclear stance.

It was unclear if Obama's words influenced the sentencing, which cannot be appealed and is the maximum allowed under North Korean law. "The North Koreans meted out a verdict somewhat harsher than I had expected," Lee Woo-young, a North Korea specialist at the University of North Korea Studies in Seoul, told The New York Times. "But ultimately the verdict doesn't mean much because this has to be resolved politically in the end."

Lee's and Ling's families made public pleas for the journalists' release last week before the start of the five-day trial. Lisa Ling said she hopes the women's predicament will serve as a catalyst for diplomacy between the countries.

"Our issue is a humanitarian issue, and we hope that our two countries that don't have a diplomatic relationship can come together to resolve this and try and get the girls released," she said.