ANDREWS AIR FORCE BASE: President Barack Obama vowed Friday to “stand fast” against anti-US violence in the Arab world, as he witnessed the return to US soil of the remains of four Americans killed in Libya.

“Their sacrifice will never be forgotten, we will bring to justice those who took them from us. We will stand fast against the violence on our diplomatic missions,” Obama said at Andrews Air Force base outside Washington.

US ambassador to Libya Chris Stevens, information officer Sean Smith, and former navy seals Tyrone Woods and Glen Doherty were killed when a mob torched the US consulate in Benghazi on Tuesday.

Their remains were carried, one-by-one from the belly of a C-17 transport aircraft by seven marines in dress uniform, in transfer cases draped in the US flag into an aircraft hangar at Andrews Air Force base outside Washington.

A band played somber music as the cases were lifted into four black hearses parked inside the hanger before family members of the dead, officials and other dignitaries.

Obama cited the Bible verse that “greater love hath no man than this, that he lay down his life for his friends,” as he said the four “American patriots”loved their country and served it well.

“They didn't simply embrace the American ideal, they lived it, they embodied it, the courage, the hope and, yes, the idealism, that fundamental American belief that we can leave this world a little better than before.”

Earlier, Secretary of State Hillary Clinton said that the “people of Egypt, Libya, Yemen, and Tunisia did not trade the tyranny of a dictator for the tyranny of a mob.”

”Today we bring home four Americans who gave their lives for our country and our values,” she said.

Amid a fourth day of violent protests targeting US diplomatic missions in the Middle East and North Africa, the top US diplomat also called for calm.

“Reasonable people and responsible leaders in these countries need to do everything they can to restore security and hold accountable those behind these violent acts,” Clinton said.

“There will be more difficult days ahead, but it is important that we don't lose sight of the fundamental fact that America must keep leading the world. We owe it to those four men to continue the long, hard work of diplomacy.”