And the American expert in nuclear intelligence, who spoke on the condition of anonymity, said the Israelis used machines of the P-1 style to test the effectiveness of Stuxnet.

But that does not rule out the possibility that a small quantity of the gas, calculated to fall within that error margin, was diverted to test some hidden centrifuges.

Testing is being conducted with three core engines before the first full engine test in early 2013.