VIENNA - A senior U.N. nuclear expert says his team is leaving for Tehran with hopes that Iranian officials will agree to talk about suspicions that the Islamic Republic has worked - or is working - on a clandestine atomic arms program.

Herman Nackaerts of the International Atomic Energy Agency is heading a group of experts focusing on the allegations, which Iran continues to deny.

Nackaerts told reporters Sunday before boarding a flight to Tehran "the highest priority remains of course the possible military dimensions of Iran's nuclear program."

The trip is the second one in less than a month as the IAEA attempts to dent nearly four years of Iranian refusal to co-operate with its probe. IAEA experts came back from their last visit in late January with no concrete results.