Iran has yet to clarify a discrepancy in uranium quantities at a Tehran research site, a UN nuclear watchdog report said, after measurements by international inspectors last year failed to match the amount declared by the laboratory. The United States has expressed concern the material may have been diverted to suspected weapons-related research activity. UN inspectors have sought information from Iran to help explain the issue after their inventory last August of natural uranium metal and process waste at the research facility in Tehran measured 19.8 kg less than the laboratory's count. Experts say such a small quantity of natural uranium could not be used for a bomb, but that the metal could be relevant to weapons-linked tests. “The discrepancy remains to be clarified,” said the latest quarterly report on Iran by the UN International Atomic Energy Agency (IAEA), issued to member states on Friday evening. The 11-page IAEA document also showed that Iran had sharply increased its uranium enrichment drive. The report's findings sent oil prices higher.