"I think that, while the talks with Iran are going on, there is one thing that must guide the international community and that is not to let the ayatollahs win," Netanyahu's office quoted him as saying as he met US Defence Secretary Chuck Hagel here.
"We must not allow Iran, the foremost terrorist state of our time, to develop the ability to develop a nuclear weapon," Netanyahu said.
Hagel assured Israel that the US "will do what we must" and said that Washington had the same goal.
The Pentagon chief's visit to Israel came as the US and five other world powers are engaged in talks with Iran in Vienna on Tehran's disputed nuclear programme.
The talks, aimed at securing a long-term deal on the extent of Iran's nuclear activities, began on Wednesday.
Israel is strongly opposed to the negotiations and has said that it is prepared to act alone if necessary with pre-emptive strike on Iran's nuclear assets.
