CAIRO -- Libya's interior minister said Wednesday that the U.S. Ambassador to Libya, Christopher Stevens, was killed when armed Islamist militants overran the U.S. consulate in Libya’s second largest city, in a day of rage that also struck the U.S. Embassy in Cairo, where demonstrators hauled down the American flag, tore it to pieces and burned it.

Secretary of State Hillary Clinton confirmed Stevens' death and said that three other Americans had died, including another diplomat, Sean Smith. The names of the other dead were withheld, pending notification of relatives, Clinton said.

"Our hearts go out to all their families and colleagues," Clinton said in a statement.

At the Pentagon, Defense officials said a Fleet Anti-terrorism Security Team of about 50 Marines was on it's way to Benghazi, though there was no estimate on when they would arrive.

The official said there was no U.S. Marine security detail at the consulate because consulates don't get U.S. Marine security.

"That's usually reserved for embassies," the official, who spoke on condition of anonymity said.

Another Defense official, also speaking on condition of anonymity, said the U.S. embassy in Tripoli has a security team of 18 Marines.

Speaking at the State Department, Clinton said that U.S. and Libyan security personnel battled the attackers together, and that the Obama administration now is working with the Libyan government to identify and track down the assailants.

The United States "will not rest until those responsible for these attacks are found and brought to justice," she said.

The administration, she said, will continue supporting the Libyan government as it struggles to surmount serious insecurity in the aftermath of the civil war that overthrew Gadhafi.

"This was an attack by a small and savage group, not the people or government of Libya," she said.

She praised Stevens as a dedicated diplomat who she first appointed as U.S. envoy to the opposition groups that fought Gadhafi and then as the U.S. ambassador to the new government.

Stevens, she said, "risked his life to stop a tyrant and then risked his life" working to rebuild Libya.

Clinton later joined Obama at the White House as the president condemned the "shocking and outrageous attack" and praised Stevens and other dead U.S. officials as "extraordinary Americans."

Speaking in the Rose Garden, Obama said that the Libyan government was working with the United States to boost security for U.S. diplomatic personnel in the country and track down the assailants, and that security was being increased at U.S. missions around the world.

Obama criticized the film that prompted the protest, but he said that nothing justified the consulate assault.

"Since our founding, the United States has been a nation that respects all faiths. We reject all efforts to denigrate the religious beliefs of others," he said. "But there is absolutely no justification for this type of senseless violence. None. The world must stand together to unequivocally reject these brutal acts."

Like Clinton, Obama said that the attack would not undermine U.S. support for the Libyan government.

"Libyan security personnel fought back against the attackers alongside Americans. Libyans helped some of our diplomats find safety, and they carried Ambassador Stevens' body to the hospital, where we tragically learned he had died," he said.