ABC News says U.S. Secretary of State Hillary Clinton has sent a letter to North Korea urging for the swift release of two U.S. journalists who have been detained in the communist state since March.

During an interview with the U.S. broadcaster Sunday, Clinton said she had sent a letter to Pyongyang asking for the two women journalists’ release.

Clinton said she has taken every action the U.S. thinks might produce positive results, adding that the charges against the two women are absolutely without merit or foundation.

ABC News said Clinton’s letter is the highest-level contact held between the Obama administration and Pyongyang.