U.S. 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.

Gates, who made stops in Israel and Jordan on Monday, was blunt in describing what Iran might expect if it refuses the offer of international arms control talks this year, or walks away from Obama's wider offer of better relations with Washington.

"If the engagement process is not successful, the United States is prepared to press for significant additional sanctions," Gates said. He added that the U.S. 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."

Defense Minister Ehud Barak told Gates on Monday that Israel was keeping on the table all the options regarding a response to Iran's nuclear program, indicating that a military strike is still a possibility even as Washington tries to persuade Israel to give diplomacy more time.

"We clearly believe that no option should be removed from the table. This is our policy. We mean it. We recommend to others to take the same position but we cannot dictate it to anyone," Barak told reporters as he stood alongside Gates during a Jerusalem press conference.

Israeli officials have said little about what military action they might have in mind. But the country has conducted a number of military exercises widely seen as possible preparations, including long-range air force maneuvers and recent movement of Israeli warships and submarines through the Suez Canal, the quickest route to the Persian Gulf from Israel.

But, Barak said, priority should be given to diplomacy and possibly tougher sanctions against Iran.

Gates's visit to Israel was partially aimed at dissuading Israel from taking any military action and buying time for U.S. diplomacy to bear fruit. However, Barak's no-options-off comment - repeated three times - seemed to indicate Gates made no visible headway in getting Israel to soften its line.

Barak's no-options-off comment - repeated three times - seemed to indicate Gates made no visible headway in getting Israel to soften its line.

Still, the comments did not signal a major rift with the U.S., which has also said there is a time limit for its diplomatic outreach. Israel has shown little enthusiasm for a global diplomatic effort that so far has failed to persuade Tehran to curb its nuclear program.

Gates, for his part, said that U.S. President Barack Obama, having offered to engage Iran over its disputed nuclear program, hopes for a response to the overture by late September.

Gates says the United States will seek much tougher United Nations sanctions on Iran if they spurn the offer of talks over the nuclear program.

"I think that the president is certainly anticipating or hoping for some kind of response this fall, perhaps by the time of the U.N. General Assembly," Gates told reporters.

The annual United Nations parley takes place in late September.

Gates said sanctions were a possibility if diplomacy fails, while also mentioning plans for a loosely defined defense umbrella meant to protect U.S. allies in the region.

"We will continue to ensure that Israel has the most advanced weapons for its national defense," he said.

Barak stressed that the schedule for U.S.-led engagement with Iran should be kept short.

The U.S. and Israel believe Iran is attempting to develop atomic weapons. Israel sees a nuclear-armed Iran as an existential threat, particularly in light of bellicose comments from Iran's President Mahmoud Ahmadinejad and Tehran's support for violent anti-Israel militant groups. Iran says its nuclear program is exclusively aimed at producing electricity.

Prime Minister Benjamin Netanyahu later met with Gates in what his office described as a "highly positive atmosphere." The two discussed a comprehensive range of bilateral, diplomatic, defense and strategic issues.

A large part of the discussion was devoted to Iran. Secretary Gates stated that the U.S. and Israel see eye to eye regarding the Iranian nuclear threat and explained that the U.S. engagement with Tehran will not be open ended.

Netanyahu reiterated the seriousness to which Israel views Iran?s nuclear ambitions and the need to utilize all available means to prevent Iran from achieving a nuclear weapons capability.