The United States on Sunday commemorated the 15th anniversary of the deadly Sept. 11, 2001 attacks in which nearly 3,000 people lost their lives.
The ceremony at the 9/11 Memorial plaza in Lower Manhattan began with the recital of the names of the dead, the tolling of church bells and a tribute in light at the site where New York City's twin towers collapsed.
During the ceremony the names of the victims were read slowly by their relatives as music was played, which paused for six moments of silence.
Four of those marked the exact times four hijacked planes crashed into the World Trade Center, the Pentagon near Washington D.C., and a Pennsylvania field. The last two took place when the North and South towers of the Trade Center collapsed.
The ceremony was held by two reflecting pools with waterfalls which now stand in the towers' former footprints, and watched over by an honour guard of police and firefighters.
US presidential candidates Hillary Clinton and Donald Trump temporarily paused their bitter election campaign to attend the service with police and relatives of the victims at the September 11 memorial.
More than 340 firefighters and 60 police were also killed on that sunny Tuesday morning in 2001, in the worst attack on US soil since Pearl Harbor was bombed in 1941.
Many of them died while running upstairs in the hope of reaching victims trapped on the towers' higher floors.
‘Darkest days’ in US history
In his weekly radio address on Saturday, US President Barack Obama said 9/11 had been one of the darkest days in the history of the nation, but that it underlined the core values and resilience that define Americans.
"We're still the America of heroes who ran into harm's way; of ordinary folks who took down the hijackers; of families who turned their pain into hope," Obama said.
We are still the America that looks out for one another, bound by our shared belief that I am my brother's keeper, I am my sister's keeper.
No public officials spoke at the New York ceremony, in keeping with a tradition that began in 2012.
The 9/11 Memorial Museum, which sits in the plaza surrounded by white oak trees, was opened on Sunday only to family members of the victims.
Houses of worship throughout the city were asked to toll their bells at 1246 GMT, the time American Airlines Flight 11 slammed into the North Tower.
A second pause came at 1303 GMT, when United Airlines Flight 175 struck the South Tower. American Airlines Flight 77 hit the Pentagon at 1337 GMT, then the South Tower collapsed at 1359 GMT.
At 1403 GMT United Airlines Flight 93 crashed near Shanksville, Pennsylvania, and the final moment of silence was observed at 1428 GMT when the North Tower fell.
Nineteen hijackers died in the attack, later claimed by Osama bin Laden and Al Qaeda, which directly led to the US war in Afghanistan and indirectly to the invasion of Iraq.