The head of the United Nations nuclear test ban treaty organization says it should take at most five years for Israel to ratify the treaty — and he thinks Iran will also ratify but the timing is uncertain.

Lassina Zerbo said in an interview Wednesday with The Associated Press that he put five years as the limit "based on the positive sign that I'm seeing from Israel," where he met Prime Minister Benjamin Netanyahu for the first time during a visit in June.

Israel and Iran are among the eight countries that must ratify the treaty before it can enter into force.

Zerbo cited the impact of the Iran nuclear deal in the Middle East for "creating the confidence-building conditions in the region to help others to move forward."