A senior U.N. nuclear inspector describes Iran's decision to answer some questions about its alleged work on nuclear weapons as encouraging.

But Tero Varjoranta said Monday a "lot of outstanding issues" remain before he can accept Iran's insistence that it did not try to make such arms.

Iran agreed Sunday to provide information on experiments with a type of detonator the U.N.'s International Atomic Energy Agency says could be used to trigger a nuclear explosion.

It also said it would answer agency questions on its laser enrichment program. The agency wants to know whether Iran continues with that activity outside of uranium enrichment with centrifuges, which the IAEA is monitoring.

Enriched uranium can make both reactor fuel and the core of nuclear weapons. Iran denies any interest in such arms.