President Obama honored victims of the 9/11 attacks and their families at the Pentagon on Thursday. (AP)

President Obama observed the 13th anniversary of the Sept. 11, 2001 attacks at the Pentagon Thursday, telling survivors, family members of those who died and others that America endures in the resolve and optimism of its people.

Obama solemnly marked "13 years since the peace of an American morning was broken, 13 years since nearly 3,000 beautiful lives were taken from us."

Standing at a memorial to to those who died, Obama said that the nation has been inspired by the determination of families to carry on in the face of unfathomable loss. They have, he said, turned this date "into something that those who attacked us could never abide," choosing hope over fear and love over hate.

"They sought to break our spirit and prove to the world that their power to destroy was greater than our power to persevere and to build. But you, America, proved them wrong," Obama said.

The United States, Obama said, is able to persevere because it is not intimidated.

"We carry on because as Americans we do not give into fear. Ever,” Obama said.

U.S. President Barack Obama pauses during a moment of silence at the Pentagon in Washington September 11, 2014. REUTERS/Gary Cameron (UNITED STATES - Tags: POLITICS MILITARY DISASTER ANNIVERSARY)

Earlier in the morning Obama, First Lady Michelle Obama and Vice President Joe Biden observed a moment of silence on the White House South Lawn. Flags flew at half-mast. After a full minute of silence, taps was played.

Obama praised the generation that "answered our nation's call" during nearly a decade of war, and paid honor to the thousands of American servicemen and women who died there.

Obama noted that the combat mission in Afghanistan will come to the end at the end of the year, but said nothing about airstrikes in Iraq and the open-ended plan he announced Tuesday night to battle the Islamic State there and in Syria.

Instead, Obama noted that there are now teenagers who were born after Sept. 11 -- a generation that, while they do not remember the attacks, were shaped by them, and by the aftermath.

“Thirteen years after small and hateful minds conspired to break us, America stands tall and America stands proud," he said. "And guided by the values that sustain us we will only grow stronger.”