President Barack Obama has been "incredibly calm, incredibly steady, and incredibly measured" in his handling of the anti-US protests in the Muslim world, a top official said Sunday.

The robust defense of the president from US ambassador to the United Nations Susan Rice follows criticism from Republican opponents that Obama's leadership is weak and has encouraged extremists to exploit the Arab Spring.

"What we've seen is that the president has been incredibly calm, incredibly steady, and incredibly measured in his approach to this set of developments," Rice told ABC's "This Week" program.

"His interventions, his leadership, has ensured that in Egypt, in Yemen, in Tunisia, in Libya, and many other parts of the world, that leaders have come out and made very plain that there's no excuse for this violence."

Republican presidential nominee Mitt Romney urged a tough line Saturday on Egypt amid deadly anti-US violence in the region, as his election running mate Paul Ryan called for greater "moral clarity" in Obama's foreign policy.

Romney toned down his rhetoric Thursday after several negative headlines and complaints from within his own party that he had made an ill-timed mischaracterization of Obama's handling of rapidly escalating events.

But on Friday Romney's pick for vice president, Ryan, led a withering attack on Obama's foreign policy, accusing it of diminishing America's global standing and of emboldening extremists.

"Peace, freedom, and civilized values have enemies in this world, as we have been reminded by events in Egypt, Libya, and Yemen," Ryan told the conservative Values Voter Summit in Washington.

Rice hit back at claims the administration was "impotent" and insisted that the demonstrations involved only a small number of people and that the United States was still broadly popular in the Muslim world.

"President Obama picked up the phone and talked to President (Mohammed) Morsi in Egypt. And as soon as he did that, the security provided to our personnel in our embassies dramatically increased," she said.

"We're not impotent, were not even less popular."

Obama leads Romney by a significant margin in surveys of who voters trust more to conduct US foreign policy. On November 6, the American people will decide whether to re-elect Obama or insert Romney into the White House.