VIENNA - The UN nuclear watchdog sought in talks with Iran on Tuesday to advance a long-stalled investigation into Tehran's atomic activities, but it was not immediately clear whether any headway was made.A spokeswoman for the International Atomic Energy Agency confirmed the two sides met in Tehran, but said the IAEA was not planning to issue a statement about the talks on Tuesday, leaving open the possibility one might be made later.Diplomatic sources had said the Vienna-based UN agency and Iran were expected to discuss IAEA requests for information about detonators that can, among other things, be used to set of a nuclear explosive device.It could have provided an opportunity for progress on a key issue ahead of a quarterly IAEA report on Iran's nuclear program, due this week, which will be debated by the U.N. agency's 35-nation governing board at a meeting in early June.