It has been nine years since two planes crashed into the Twin Towers of the World Trade Center in New York. The 9/11 attacks have been remembered throughout the city with a series of memorials. Similar commemorations were also held in Washington DC and Pennsylvania.

A day of mourning for nearly 3-thousand 9/11 victims began in New York with moments of silence and streams of tears.

Family members gathered at a park, before visiting Ground Zero to lay flowers and pay tribute to their lost loved ones.

Local officials opened the ceremony by calling for a minute's silence to pay respect to victims of the tragedy.

Michael Bloomberg, New York Mayor, said, "No other public tragedy has cut our city so deeply. No other place is as filled with our compassion, our love, and our solidarity."

Several moments of silence were observed to mark the different times of the attacks at the former sites of the World Trade Center's north and south towers.

Relatives also mourned those killed by reading their names out aloud. A little girl, whose uncle died in the attacks, delivered a heart-felt speech at the ceremony.

"......God bless America."

On the same day, President Barack Obama honored those who lost their lives in the attacks with a private moment of silence at the White House.

Later, he laid a wreath at a ceremony at the Pentagon, where 184 people died nine years ago to the day.

US President Barack Obama said, "Nine years have now passed. In that time, you have shed more tears than we will ever know. And though it must seem some days as though the world has moved on to other things, I say to you today that your loved ones endure in the heart of our nation, now and forever."

The President has said the fate of Osama bin Laden, who masterminded the attacks, is still extremely important to national security.

Obama said it remains a high priority to capture or kill the terrorist leader, and the country's intelligence forces are working night and day to make that happen.