Rivals for the White House have displayed a moment of unity as the US marks the 19th anniversary of the 11 September 2001 terrorist attacks.
Democratic presidential nominee Joe Biden greeted Vice-President Mike Pence at the Ground Zero memorial in New York, where each attended ceremonies.
Mr Biden then travelled to Shanksville, Pennsylvania – the site of the Flight 93 memorial – to pay respects.
President Donald Trump spoke there earlier on Friday.
However Mr Biden and Mr Trump did not cross paths because their schedules did not overlap.
Nearly 3,000 people died when four hijacked airliners were crashed into the World Trade Center in New York, the Pentagon and – after passengers fought back – the field in Shanksville, on what is the worst terrorist attack in US history.
How is President Trump marking the anniversary?
Joined by First Lady Melania Trump, Mr Trump attended a morning service at the Shanksville memorial, where Flight 93 crashed after its 40 passengers and crew prevented al-Qaeda hijackers from reaching the US Capitol building.
“To the family members of Flight 93: today every heartbeat in America is wedded to yours,” Mr Trump said. “Your pain and anguish is the shared grief of our whole nation.”
“The memory of your treasured loved ones will inspire America for all time to come. The heroes of Flight 93 are an everlasting reminder that no matter the danger, no matter the threat, no matter the odds, America will always rise up, stand tall and fight back.”
Where is Biden?
Mr Biden and his wife, Jill, attended a memorial service and commemoration ceremony at the 9/11 museum in New York City.
They travelled to Shanksville in the afternoon to visit the same memorial as Mr Trump. Mr Biden was seen greeting family members of those killed in the attack.
He and his wife laid a wreath on the memorial as well.
Mr Biden greeted Mr Pence at the World Trade Center site in New York earlier in the day, and the pair touched elbows in lieu of a handshake to observe protocols aimed at preventing the spread of coronavirus.
Mr Biden referenced the pandemic in a series of tweets later in the day, saying: “This year, we mark the anniversary of 9/11 in the midst of another crisis that compels us to summon the best of the American people in the face of unconscionable, inconceivable loss.”
Mr Pence delivered short remarks in New York City and read passages from the Bible, saying: “I pray these ancient words will comfort your hearts and ours.”
What happened on 9/11?
The 9/11 attacks were a series of four coordinated attacks on the US by the Islamist terror group al-Qaeda in which about 3,000 people were killed on 11 September 2001, some 400,000 people were injured or exposed to other contaminants in the aftermath of the attacks, according to the US Centers for Disease Control.
Hundreds of first responders and survivors have died in the years since due to related illnesses, like cancer.
Weeks after the attack, the US sent troops to Afghanistan to combat al-Qaeda. The so-called ‘War on Terror’ has stretched decades and American intervention in the Middle East continues to be a quagmire of US foreign policy.