Israeli opposition leader Tzipi Livni urged US Defence Secretary Leon Panetta to ratchet up sanctions against Iran "without delay," a statement from her Kadima party said on Saturday.
It said that the two met in Washington on Friday. Israeli media said that the meeting took place before Panetta delivered a speech urging Israel to break out of growing regional "isolation" by repairing diplomatic ties with Egypt and Turkey, and renewing peace efforts with the Palestinians.
"The world needs to stop Iran," the Kadima statement quoted Livni as telling Panetta. "Stronger, tougher sanctions are required without delay."
Israel - and much of the international community - fear that Iran's nuclear programme masks a drive for a weapons capability. Tehran denies any such ambition and says the programme is for peaceful civilian energy and medical purposes only.
In his comments on Friday to the Brookings Institution's Saban Centre for the Middle East, a Washington think-tank, Panetta vowed to prevent Iran from obtaining nuclear weapons, saying the Obama administration had not ruled out possible military action.
But he warned of the potential downside of any strike, which he said could actually strengthen the Tehran regime while not necessarily destroying all targets.
The Pentagon chief said he understood Israel's anxieties over turmoil in the Middle East but said the Arab Spring offered an opportunity for the country to forge a more secure place in the region.
It was crucial for Israel to reach out and "mend fences" with countries such as Turkey, Egypt and Jordan that share an interest in regional stability, said Panetta, who issued similar appeals in a visit to the region in October.
Israel also needed "to lean forward on efforts to achieve peace with the Palestinians," Panetta said.
Livni said that neutralising Iran and making peace with the Palestinians were both factors for Middle East stability.
"The struggle against a nuclear Iran, and renewed movement in negotiations with the Palestinians will strengthen the pragmatic camp in the region," she told Panetta.