Video of protesters cheering in the night as flames billowed from the consulate were a stunning image after years in which Tehran's influence among Shi'ite Muslims in Arab states has been a defining factor in Middle East politics.

Recent weeks have seen mass protests and clashes erupt in far-flung places triggered by seemingly minor actions that each came to be seen as the final straw.

"We regret the unintentional loss of civilian lives ... and express our deepest sympathies to the families and others affected by these strikes," the Pentagon said in a statement.