North Korea’s top court has sentenced two American journalists, Laura Ling and Euna Lee, to 12 years jail with hard labor for illegally entering the reclusive country to film a documentary.

The sentencing came amid soaring tensions between the Washington and the Democratic People’s Republic of Korea (DPRK) fueled by the North’s latest nuclear and missile tests.

In a brief, two-sentence report, Korean Central News Agency, North Korea’s official state-run media organization, said Laura Ling, 32, and Euna Lee, 36 were guilty of a “grave crime” against the nation and of illegally crossing into North Korea.

Ling and Lee were working for former vice president Al Gore’s California-based Current TV and cannot appeal the verdict because they were tried in North Korea’s highest court, where decisions are final.

Kim Yong-hyun, a professor at Seoul’s Dongguk University, said the 12-year sentence, the maximum possible allowed under North Korea’s laws, could have been a reaction to “hard-line” moves by the U.S., including threats of sanctions and putting North Korea back on a list of state sponsors of terrorism.

Tension has been running high since North Korea held its second underground nuclear test on May 25 and followed it up with several missile tests.

The circumstances surrounding the trial of the two journalists and their arrest on March 17 on the China-North Korean border have been shrouded in secrecy.

The trial was not open to the public or foreign observers, including the Swedish Embassy, which looks after American interests in the DPRK.

The two were filming a documentary on the trafficking of women at the time of their arrest, and it’s unclear if they strayed into North Korea or were grabbed by aggressive border guards who crossed into China.

US State Department spokesman Ian Kelly said Washington was trying to confirm press reports of the sentencing.

Kelly said the US was “deeply concerned” about the sentences and that officials will “engage in all possible channels” to free the women.