President Obama and Mitt Romney suspended their negative advertising on Tuesday, the 11th anniversary of the Sept. 11, 2001 terrorist attacks.

“On this most somber day, those who would attack us should know that we are united, one nation under God, in our determination to stop them and to stand tall for peace and freedom at home and across the world,” Romney said in a statement.

The Republican presidential nominee was scheduled to speak Tuesday morning at the National Guard Association Convention in Reno, Nev.

The president and First Lady Michelle Obama held a moment of silence on the South Lawn of the White House before attending a ceremony at the Pentagon. President Obama also was scheduled to visit the Walter Reed National Military Medical Center.

Vice President Joe Biden spoke at the Flight 93 National Memorial Commemorative Service in Shanksville, Pa., and Romney’s running mate, Paul Ryan, planned to spend the day at home in Janesville, Wis.