A large piece of airplane debris found close to the World Trade Center site in New York is believed to be landing gear from one of the planes which struck the twin towers in 2001.
The metal part has cables and levers on it and is about 3 feet wide and 1.5 feet deep.
New York Police Department Commissioner Ray Kelly said that it includes a clearly visible Boeing identification number.
Mr Kelly said the medical examiner would check the area around the site to see if it was toxic in any way.
"They will also check to see if there's any human remains at the site and then a determination will be made as to how to move the part from that location".
New York Police Department (NYPD) confirmed that the five-foot-long part was discovered by building surveyors between two buildings on the site where a mosque and community center has been proposed three streets away from Ground Zero.
The part bears a "Boeing" stamp, followed by a series of numbers.
Police spokesman Paul Browne said the NYPD had secured the location and would treat it as a crime scene.
US presidential candidates Barack Obama and Mitt Romney have both tweeted on America's commitment to freedom, 11 years on from the 9/11 terrorist attacks.
As painful as this day is and always will be, it leaves us with the lesson that no act of terrorism can ever change what we stand for. -bo
On this most somber day, America is united under God in its quest for peace and freedom at home and across the world.
US President Barack Obama has told 9/11 victims' families that the whole country shares their loss on the 11th anniversary of the terrorist attacks.
Speaking at the Pentagon, where 184 people were killed, Mr Obama said:
Eleven times we have paused in remembrance and reflection, in unity and in purpose. This is never an easy day, but it is especially difficult for all of you, the families of nearly 3,000 innocents who lost their lives.
But no matter how many years pass, no matter how many times we come together on this hallowed ground, know this: That you will never be alone, your loved ones will never be forgotten.
They will endure in the hearts of our nation because through their sacrifice they helped us make the America we are today, an America that has emerged even stronger.
US President Barack Obama has said the annual act of remembrance for the victims of the 9/11 attacks provides the chance to recommit the nation's values.
In an address at the Pentagon in Washington, Mr Obama said: "No act of terrorism can change what we stand for."
President Barack Obama and First Lady Michelle Obama have led a ceremony of remembrance at the White House on the 11th anniversary of the 9/11 terrorist attacks.
Families of the victims of the 9/11 attacks in New York paid tribute to their loved ones during a ceremony at Ground Zero.
It is 11 years ago today that the attacks killed nearly 3,000 people.
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The 70,000 surviving firefighters, police officers and other first responders who raced to the World Trade Center after the attacks on September 11th, will be entitled to free monitoring and treatment for some 50 forms of cancer.
While other illnesses have long been covered by a compensation scheme, there has been a long debate over including cancers.
The National Institute for Occupational Safety and Health has said that responders as well as survivors exposed to toxic compounds from the wreckage, which smoldered for three months, will be covered for cancer under the Zadroga 9/11 Health and Compensation Act.
Illnesses related to the attacks have caused an estimated 1,000 deaths. Last week, the New York City Fire Department etched nine more names into a memorial wall honouring firefighters who died from illnesses after their work at Ground Zero, bringing the total to 64.
The names of those who lost their lives in the September 11th terror attacks in 2001 as well as those who died in the 1993 attack will be read by family members, at the site of the World trade Center.
There will be pauses for six moments which mark the timeline of the 9/11 attacks which left 2,998 dead.