U.N. Secretary General Kofi Annan expressed grave concern Thursday over the future of the nuclear nonproliferation treaty, saying it is facing a crisis and could collapse.

"The (Nonproliferation Treaty) regime faces a twin crisis -- of compliance and of confidence," Annan told an audience at the University of Tokyo in the afternoon during a ceremony in which he was conferred an honorary doctorate.

"The regime will not be sustainable if many more countries develop the most sensitive phases of the fuel cycle, and are equipped with the technology to produce nuclear weapons at short notice," Annan said.