A prominent Syrian dissident ex-lawmaker who the United States had urged be allowed to travel abroad for medical treatment was arrested, a Syrian human rights group said Tuesday. Riad Seif was taken into custody Monday evening by security authorities, the Syrian National Organization for Human Rights in Syria said in a statement. The statement, e-mailed to The Associated Press, did not give details of the arrest but said a warrant had been issued earlier against Seif for participation in a December meeting of dissidents. There was no official confirmation of the arrest from the Syrian government. Syria rarely comments on security measures against activists. In Washington, the State Department denounced Seif's arrest and called for his immediate release along with other detainees arrested "simply for their desire to speak their minds and engage in a political dialogue in Syria."