The New York authorities have rejected a request from Iranian President Mahmoud Ahmadinejad to visit the site of the 11 September 2001 attacks.
The US said it would not allow Mr Ahmadinejad a "photo op"
The Iranian president will arrive in New York on Sunday to address the United Nations General Assembly.
A New York police spokesman said the World Trade Center site was closed to visitors because of construction work.
He said requests by Mr Ahmadinejad to visit Ground Zero would be opposed on security grounds.
New York Police Deputy Commissioner Paul Browne said the Iranian leader had asked the permission of the police department, the US Secret Service and the Port Authority of New York and New Jersey to visit the site.
White House spokesman Gordon Johndroe told reporters it seemed "more than odd that the president of a country that is a state sponsor of terror would visit Ground Zero".
And Zalmay Khalilzad, the United States ambassador to the UN, told journalists that the US would not support Iran using the site for a "photo op".
But a spokesman for the Iranian mission to the UN said they were still hopeful of finding some way for Mr Ahmadinejad to pay respect to the victims of the 2001 attacks.
Tensions between the US and Iran are high amid Washington's claims that Tehran is arming militants in Iraq and seeking to develop nuclear weapons.