A six-year probe has not ruled out the possibility that Iran may be running clandestine nuclear programs, the chief U.N nuclear inspector said Monday, urging Iran to reassure the world by ending its secretive ways.

At the opening session of the International Atomic Energy Agency''s 145-nation conference, the European Union also urged Tehran to fully cooperate with a U.N. probe that is trying to assess all of its past and present nuclear activities.

"The international community cannot accept the prospect of Iran acquiring nuclear weapons," the EU said in a statement.

Israel also took Iran to task for co-sponsoring Islamic attempts to label the Jewish state a nuclear danger to the Middle East.

"What moral standing poses sponsors of this agenda item, who do not recognize Israel''s right to exist while criticizing Israel policies aiming at securing its very existence?" asked Israeli delegate Schaul Chorev.