A senior Iranian negotiator said "serious issues" continue to divide Tehran and world powers in talks over the country's nuclear drive after a "very useful" session in Geneva Thursday morning. "We had a very useful, intensive discussion" over "content and details" with representatives of the so-called P5+1 countries and their chief negotiator, EU foreign policy chief Catherine Ashton, ISNA news agency quoted Abbas Araqchi as saying. However, "some serious issues continue to be a source of difference over which we had serious discussions," Araqchi added.