WASHINGTON (AP) — For President Barack Obama, the prospect of more U.S. military action in the Middle East hangs over his observance today of the anniversary of the September 11th attacks. During a ceremony at the Pentagon, he vowed to "defend our nation" against the threats that endure, even though they may be different than the ones that faced the country 12 years ago today. He said, "Let us have the wisdom to know that while force is sometimes necessary, force alone cannot build the world we seek." Among those gathered at the Pentagon were family members of those killed 12 years ago today. Many wore red, white and blue striped ribbons, and some cried as the president spoke. Obama said, "Our hearts still ache for the futures snatched away, the lives that might have been." The president also paid tribute to the four Americans who were killed one year ago today in an attack on a U.S. compound in Benghazi, Libya. He asked the country to pray for those who "serve in dangerous posts." Obama began the day with a somber remembrance at the White House. Along with first lady Michelle Obama, Vice President Joe Biden and wife Jill Biden, Obama stood on the South Lawn to observe a moment of silence at 8:46 a.m., the moment when the first plane hit the World Trade Center.