another as he heads to russia. tillerson emphasized the trump white house puts a top priority on fighting isis. >> we believe the syrian people will ultimately be able to decide the fate of bashar al assad. >> reporter: white house spokesman sean spicer acknowledging both goals. >> we all recognize that that happens and there can be a multi-pronged approach. we're ensuring that isis is contained and there's a de-escalation of the proliferation of chemical weapons at the same time creating the environment for a change in leadership. >> reporter: tillerson attending the g7 foreign ministers meeting in italy says the world cannot stand by and watch. state department officials tell cnn tillerson's message in moscow, russia bears responsibility for assad's actions. and there may be more leverage as a dossier of responsibility for the nerve agent attack takes shape. according to u.s. officials,