Israel's defence minister Ehud Barak has that warned Israel never promised the US it would hold off from attacking Iran while nuclear talks were taking place.
Barak told Israel's Army Radio that he did not believe the talks with Iran would prevent it from developing nuclear power.
Instead the minister said Israel regretted the time that was being lost. It was precious, he said. Barak admitted he would be happy to be proved wrong.
In a separate interview from Colombia he said: "I do not believe the efforts of the international community to stop Iran's nuclear programme will bear fruit."
His comments confirm the growing rift between Israel and its long-time ally, the United States.
Both countries have demanded that Iran stops its uranium enrichment programme but Israel has openly refused to rule out a military strike on the country's nuclear facilities. Officials have said several times that "all options are on the table".
The US has been pushing for a diplomatic solution and insists that talks are vital to find a solution.
US Secretary of State Hillary Clinton warned Iran that the US would maintain sanctions against it and called for the Ahmadinejad government to think about what it could bring to the table for the next round of talks, in Baghdad on 23 May.
Iran's foreign minister, Ali Akbar Salehi, said he was confident progress could be made following the last round of talks in Istanbul but said a goodwill gesture from the West could encourage Iran.
"If the West wants to take confidence-building measures it should start in the field of sanctions because this action can speed up the process of negotiations," he told Iranian student news agency ISNA.
"If there is goodwill, one can pass through this process very easily. We are ready to resolve all issues very quickly and simply in the Baghdad meeting."