Rafael Grossi, the head of the International Atomic Energy Agency (IAEA), on Monday said Iran has failed to answer questions about the discovery of uranium particles at former undeclared sites in the country, and urged Tehran to provide information "without further delay."

"I think it's becoming increasingly difficult," Grossi said when asked how likely it is that the IAEA will again extend a monitoring deal with Iran later this month. The two sides announced on May 24 that they were extending the three-month accord by a month.

(With input from AP, Reuters)