VIENNA (AP) — The U.N.’s nuclear watchdog says it has identified three locations in Iran where the country possibly stored undeclared nuclear material or undertook nuclear-related activities without declaring it to international observers.

The International Atomic Energy Agency said Tuesday in a confidential report to member nations seen by The Associated Press that it has sent questions to Iran in three separate letters but has received no reply.

“The agency identified a number of questions related to possible undeclared nuclear material and nuclear-related activities at three locations in Iran that had not been declared by Iran,” the agency said in a report.

The IAEA had previously said that uranium particles of man-made origin had been discovered at one location outside Tehran that had not been declared, which appeared to confirm allegations made by the U.S. and Israel about a secret nuclear warehouse.