Palestinian-Syrian Bassel Khartabil was detained by the Syrian government in 2012, a year after Arab Spring protests first broke out. His wife Noura Ghazi is said to have announced that he was secretly executed in late 2015.
"We extend our deepest and heartfelt condolences to his family, friends, and loved ones," the State Department Deputy spokesperson Heather Nauert said.
"The United States expresses its outrage over the repeated acts of brutality, including torture, and extra- judicial executions, conducted by the Syrian regime," she said.
"Every day, courageous individuals work to recover from the devastation the Syrian regime has wrought, and the United States will continue to stand with them as Syrians work towards a negotiated political settlement that brings an end to the conflict," said the State Department spokesperson.