Vienna - UN nuclear inspectors have found no "concrete proof" that Iran's nuclear program is of a military nature, a senior official close to the UN nuclear agency said Thursday. "Inspectors have not uncovered any concrete proof that Iran's nuclear program is of a military nature," the official told reporters on condition of anonymity.

The official said this conclusion came as inspectors from the Vienna-based International Atomic Energy Agency (IAEA) were investigating "additional questions about the scope and nature of Iran's nuclear program" as part of an ongoing investigation since February 2003.

These questions have involved Iran's work with sophisticated P2 centrifuges to enrich uranium and blueprints Iran possesses to make nuclear weapons parts.

Iran has not been forthcoming in answering these questions.

"There is a standstill with regard to the resolution of outstanding issues which would clarify the peaceful nature of Iran's program," the official said.