JERUSALEM: Israel hardened its insistence Monday that it would do anything it felt necessary to stop Iran from getting a nuclear bomb, just the ultimatum the United States hoped not to hear as it tried to nudge Iran to the bargaining table.

US Defense Secretary Robert Gates reassured Israel that the new Obama administration was not naive about Iran's intentions, and that Washington would press for new, tougher sanctions against the Iranians if they balk. He didn't say what those might include.

US Defense Secretary Robert Gates, right, meets with Israeli Prime Minister Benjamin Netanyahu in Jerusalem Monday, July 27, 2009.[Agencies]

Israeli Defense Minister Ehud Barak used a brief news conference with Gates to insist three times that Israel would not rule out any response -- an implied warning that it would consider a pre-emptive strike to thwart Iran from obtaining nuclear weapons.

"We clearly believe that no option should be removed from the table," Barak said. "This is our policy. We mean it. We recommend to others to take the same position, but we cannot dictate it to anyone."

The question of how to deal with Iran's rapid nuclear advancement has become a notable public difference between the new administrations in Jerusalem and Washington, despite overall close relations. Israel considers itself the prime target of any eventual Iranian bomb.

Iran says it is merely trying to develop nuclear reactors for domestic power generation. Israeli leaders fear the US prizes its outreach to Iran over its historic ties to Israel and appears resigned to the idea that Iran will soon be able to build a nuclear weapon.

Obama says he has accepted no such thing. Still, the United States argues that an Israeli attack against Iran would upset the fragile security balance in the Middle East, perhaps triggering a new nuclear arms race and leaving everyone, including Israel and Iran, worse off.

Gates emphasized areas of agreement with Israel, including that the offer of talks with Iran must not be open-ended.

"If the engagement process is not successful, the United States is prepared to press for significant additional sanctions," Gates said. He added that the US would try to abandon the current policy of gradual international pressure, where layers of generally mild sanctions have been added each time Iran has flouted international demands.

"We would try to get international support for a much tougher position," Gates said.

"Our hope remains that Iran would respond to the president's outstretched hand in a positive and constructive way, but we'll see."