The head of the UN nuclear watchdog agency has called on Iran to explain tunnels built around a nuclear site, but remains optimistic about the US-Iran talks on Iran's nuclear program. Rafael Grossi, director general of the International Atomic Energy Agency, expressed concern about Iran's lack of transparency regarding the tunnels. However, he also mentioned that Iranian and IAEA experts will meet to discuss the issue further. Grossi believes that there is a general expectation that the talks will go well and that any agreement will be verified by the IAEA.