The United States condemns \"in the strongest possible terms\" the killing of Syrian human rights activist Ghiyath Mattar while in the custody of Syrian Security Forces, State Department spokeswoman Victoria Nuland said in a statement released on Sunday night. \"We offer our deepest condolences to his family and friends as they mourn their loss,\" Nuland said. Ghiyath, along with leading activist Yahya Sharbaji and a number of other human rights activists committed to non-violent resistance, was detained on September 6, the statement noted. \"Ghiyath Mattar\'s courage in the face of the Assad regime\'s brutal repression is well known in his home of Daraya and across Syria,\" Nuland said. \"His brave commitment to confronting the regime\'s despicable violence with peaceful protest serves as an example for the Syrian people and for all those who suffer under the yoke of oppression.\" \"We stand with the Syrian people in their resistance to tyranny,\" she said. \"We call on the Assad regime to immediately cease all violence against the Syrian people and release all political prisoners. We again call on Assad to step aside and allow the Syrian people to embark upon the democratic transformation they demand.\"