Story highlights It's the 15th anniversary of 9/11

Obama delivered remarks at a Pentagon ceremony

Washington (CNN) President Barack Obama called on Americans to "reaffirm our character as a nation" as he marked the 15th anniversary of the 9/11 terror attacks during a ceremony outside the Pentagon on Sunday.

Defense Secretary Ash Carter and Chairman of the Joint Chief of Staff Gen. Joseph Dunford joined Obama in the commemoration at the National 9/11 Pentagon Memorial, outside the location of the building that was hit by a terrorist-hijacked plane.

"We honor the courage of those who put themselves in harm's way to save people they never knew. We come together in prayer and in gratitude for the strength that has fortified us across these 15 years. And we renew the love and the faith that binds us together as one American family," Obama said.

The Pentagon attack killed 184 people, including workers inside the building and passengers from hijacked American Airlines Flight 77, which crashed into it.

Obama praised the country's diversity during his remarks, calling it a strength and not a weakness.

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