"But as I said yesterday, there is no justification, none at all, for responding to this video with violence."
Protests have erupted for three days running outside US diplomatic missions in Egypt, Libya, Yemen and elsewhere by demonstrators who deem the low-budget movie Innocence of Muslims made in the United States as offensive to Islam.
US ambassador Chris Stevens and three other Americans were killed when heavily-armed extremists launched a sustained four-hour attack on the US mission in the Libyan city of Benghazi late Tuesday.
Condemning the violence, Clinton said at the launch of a strategic dialogue between the United States and Morocco that all "leaders in government, leaders in civil society or religious leaders must draw the line at violence."
"Any responsible leader should be standing up now and drawing that line," she added.
"It is especially wrong for violence to be directed against diplomatic missions. These are places whose very purpose is peaceful to promote better understanding across countries and cultures.