WASHINGTON--The United States is "deeply concerned" by North Korea's sentencing of two American journalists to 12 years in a labor camp, State Department spokesman Ian Kelly said Monday.

"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," Kelly said in a statement.

A North Korean court on Monday sentenced two female US journalists to 12 years in a labor camp for an illegal border crossing and an unspecified "grave crime," North Korean state media reported.

Laura Ling and Euna Lee were detained by North Korean border guards on March 17 along the frozen Tumen River, which marks the border with China, while researching a story about refugees fleeing the hardline communist state.

"Our thoughts are with the families of the two detained journalists at this difficult time," Kelly said.

"We once again urge North Korea to grant the immediate release of the two American citizen journalists on humanitarian grounds."

US Secretary of State Hillary Clinton said Sunday the charges against the pair were baseless and they should be allowed to return home.

Pyongyang has in the past freed captured Americans but only after personal interventions. The US State Department last week did not rule out the possibility that former vice president Al Gore might undertake such a mission.

Gore is chairman of the California station Current TV, which employs the two journalists, both aged in their 30s.

Both detainees are married and Lee has a four-year-old daughter.