US President Joe Biden has called for national unity in a speech marking the 21st anniversary of the September 11 attacks on the United States.
During a ceremony at the Pentagon on Sunday, Biden said, "I hope we'll remember that in the midst of these dark days, we dug deep, we cared for each other... and finding something all too rare, a true sense of national unity."
He also said, "We will secure our democracy together as one America."
One hundred eighty-four people were killed at the Pentagon when one of four hijacked aircraft crashed into the building.
Last month, Biden announced that the US had killed Al-Qaida leader Ayman al-Zawahiri in Afghanistan. The man is believed to have helped plot the September 11 attacks.
Biden vowed that the fight against terrorism would continue. He said, "We will not rest. We'll never forget. We'll never give up."
He also said, "We'll continue to monitor and disrupt those terrorist activities... And we'll never hesitate to do what's necessary to defend the American people."