Bill Bratton also says the risk of another devastating attack remains.
On Friday, New York will mark the 14th anniversary of the 9/11 attacks which levelled the Twin Towers of the World Trade Center, claiming nearly 3,000 lives.
Meanwhile, the US State Department says it cannot divulge any further details about yesterday's terror alert from its embassy in Pretoria.
Spokesperson John Kirby says this is an intelligence matter.