She went on to say that the Constitution did not allow the United States to “prevent these kinds of reprehensible videos from ever seeing the light of day,” and could not if it tried, given modern technology.

“There are, of course, different views around the world about the outer limits of free speech and free expression, but there should be no debate about the simple proposition that violence in response to speech is not acceptable,” she said. “We all — whether we are leaders in government, leaders in civil society or religious leaders — must draw the line at violence. And any responsible leader should be standing up now and drawing that line.”

The new violence came as news reports from Libya said the authorities there had made at least four arrests in connection with the killings of the four Americans in the mayhem that engulfed the American Consulate in the eastern city of Benghazi on Tuesday night. F.B.I. agents were also investigating the killings, a law enforcement official in Washington said.

In addition, the third of those four victims was positively identified by his family as Glen Doherty, 42, of Winchester, Mass., a former Navy SEAL working as a security officer. Mr. Doherty died along with the American ambassador to Libya, J. Christopher Stevens, and another diplomat, Sean Smith. The fourth American has not yet been publicly identified.

The killings in Libya in particular led to a major political flare-up in the United States on Wednesday, when President Obama’s Republican challenger, Mitt Romney, issued a harsh critique of Mr. Obama’s handling of the anti-American protests and accused him of apologizing for the United States. The administration rejected the accusation and even some Republicans distanced themselves from Mr. Romney’s criticism as inappropriate under the circumstances.