We have had quite a constructive meeting," said Mohamed ElBaradei of the International Atomic Energy Agency. "We are off to a good start. Most of the technical issues have been discussed and we will continue tomorrow."

His comments came after officials from Tehran had huddled with representatives of the United States, Russia and France at the IAEA headquarters in Vienna.

Monday's meetings ended before 6 p.m. (noon ET) and were slated to reconvene Tuesday at 10 a.m. (4 a.m. ET).

Participants included Iran's envoy to the IAEA, Ali-Asghar Soltaniyeh; Nikolay Spassky, deputy head of the Russian Federal Atomic Energy Agency; Frederic Mondoloni, French representative to the IAEA; and U.S. Department of Energy Deputy Secretary Daniel Poneman.

The world powers and Iran agreed in principle at the beginning of October that low-enriched uranium produced in Iran -- not weapons-grade material -- would be sent abroad for further enrichment, then returned for use in medical research and treatment.

Details of the tentative deal are expected to be worked out at the Vienna meetings, which could stretch into Tuesday, according to Javier Solana, the European Union foreign policy chief.

On October 25, UN nuclear inspectors are to visit the facility, which is located near the city of Qom.