US still fixated by nuclear terror

Views among scientists differ on whether a terror group like Al-Qaeda could build and detonate a primitive nuclear bomb on a US city.

But no president will take the threat lightly after seeing the impact of mass terrorism wreaked by the September 11 attacks in 2001.

Obama said while hosting the first nuclear summit in Washington two years ago that a nuclear strike on a major populated area could change the global security landscape for years to come.

"The ramifications economically, politically and from a security perspective would be devastating," he said.

Analysts say that Obama's concern is justified.