The head of the U.N. nuclear agency is pushing back against critics questioning the wisdom of letting Iranian experts take samples meant to help determine whether their own country clandestinely worked in the past on atomic arms.

In an interview with The Associated Press Thursday, Yukiya Amano said he is convinced the process was faultless.

Amano spoke less than a week after confirming that instead of personnel from his International Atomic Energy Agency, Iranians did the environmental sampling at a site where such alleged experiments work took place.

Noting that the Iranians were under stringent IAEA monitoring, Amano then said he was confident "so far" that the samples were genuine. He appeared to go further on Thursday, however, saying he is "very sure that ... the samples are authentic."