The official said North Korea could conduct a test "with little or no warning" but a decision to do so would be "as much political as it is technical," said the official, who spoke on condition of anonymity.
"How close they may be to pulling the chain or pressing a button is what's not clear," the official said.
The intelligence official said activity has been observed at potential test sites since the first test, but would not describe it further to protect sources and methods.
"Certainly nobody is discarding the possibility of a second test for a whole lot of reasons," the official told AFP.
"These are all real possibilities, and the activity observed could be consistent with that, but it doesn't in and of itself really get you there," he said.
He said activity at the sites was "not the decisive bellwether. And if people are working off activity alone, I'm not certain that's enough to say something's imminent."

Copyright AFP (Agence France-Presse), 2006