9/11 anniversary marked amid mosque and Koran row
The US is marking nine years since September 11 amid a polarising national debate over a mosque planned blocks from the World Trade Centre site and a pastor's threat to burn the Koran.
Thousands of protesters for and against the planned Islamic centre are expected to hold rival demonstrations after the typically sombre anniversary ceremony.
Bagpipes and drums played to open the ceremony, followed by brief comments by Mayor Michael Bloomberg.
"Once again we meet to commemorate the day we have come to call 9/11. We have returned to this sacred site to join our hearts together, the names of those we loved and lost," Mr Bloomberg 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."
A moment of silence began at 8:46am (1346 BST), the time the first hijacked jetliner hit the north tower of the World Trade Centre in 2001.
The first plane hijacked by Islamic extremists hit the centre's north tower at 8:46am in 2001. Within hours, both towers were rubble and thousands were dead there, at the Pentagon and at a crash site in Shanksville, Pennsylvania.
President Barack Obama and first lady Michelle Obama were attending separate services at the Pentagon in Washington and a rural field in Shanksville, Pennsylvania.
While the President was at the Pentagon service and the first lady was to join former first lady Laura Bush at Shanksville, Vice President Joe Biden planned to speak at the New York ceremony, where 2,752 people were killed when two jetliners flew into the World Trade Centre.