"This week in Libya, we lost four of our fellow Americans. Glen Doherty, Tyrone Woods, Sean Smith and Chris Stevens were all killed in an outrageous attack on our diplomatic post in Benghazi. These four Americans represented the very best of our country," Obama said in his weekly address.
"Glen and Tyrone had each served America as Navy SEALs for many years, before continuing their service providing security for our diplomats in Libya. They died as they lived their lives -- defending their fellow Americans and advancing the values that all of us hold dear.
"Sean also started his service in uniform, in the Air Force. He then spent years at the State Department, on several continents, always answering his country's call. And Ambassador Chris Stevens died a hero in two countries -- here in the United States, where he inspired those of us who knew him; and in Libya, a country that he helped to save, where he ultimately laid down his life.
"On Friday, I was able to tell their families how much the American people appreciated their service. Without people like them, America could not sustain the freedoms we enjoy, the security we demand, and the leadership that the entire world counts on," the president said.
"As we mourn their loss, we must also send a clear and resolute message to the world: Those who attack our people will find no escape from justice. We will not waver in their pursuit. And we will never allow anyone to shake the resolve of the United States of America."
Obama said there is "never any justification for violence."
"There is no religion that condones the targeting of innocent men and women. There is no excuse for attacks on our embassies and consulates. And so long as I am commander in chief, the United States will never tolerate efforts to harm our fellow Americans."
Obama said efforts are under way to "see that justice is done for those we lost, and we will not rest until that work is done."
"Most of all, we must reaffirm that we will carry on the work of our fallen heroes. …
"Let us never forget that for every angry mob, there are millions who yearn for the freedom, and dignity, and hope that our flag represents. That is the cause of America – the ideals that took root in our founding; the opportunity that drew so many to our shores; and the awesome progress that we have promoted all across the globe," the president said.