The chief United Nations nuclear inspector has returned to Vienna from Iran with no new agreement on investigating allegations that the country is working to develop nuclear weapons.

Herman Nackaerts, chief United Nations nuclear inspector

Herman Nackaerts led the International Atomic Energy Agency team in the latest round of talks in Tehran, but said Thursday the two sides were unable to finalize a deal.  Also, Thursday there were new indications Iran is taking new steps to rapidly advance its nuclear capabilities.