A U.S. attack on Iran's key underground nuclear facility would not be a guaranteed success, according to a national security expert.

With about 2,000 operational centrifuges, the enrichment facility produces uranium enriched to 60 per cent — a small step away from weapons-grade 90 per cent enrichment — making it a cause of concern for Israel.

Only the U.S. military has the 30,000-pound bomb capable of reaching the facility and the bomber that can carry it.