The November 24 accord in Geneva was denounced as a "historic mistake" by Netanyahu, increasing strains in an alliance already marked by his past disputes with U.S. President Barack Obama over strategy on Iran and the Palestinians.
Visiting Israel as the talks with Tehran gathered pace, Kerry met an irate Netanyahu. But they worked to affirm their friendship on Thursday: Their offices issued pictures of them smiling in private conversation, and while briefing reporters afterwards Kerry referred to Netanyahu by his nickname "Bibi".
Israel argues an easing of some sanctions on Iran before it abandons nuclear projects with bomb-making potential risks snowballing as foreign business partners rush into the breach.
"Steps must be taken to prevent a further erosion of sanctions," said Netanyahu, who has described a nuclear-armed Islamic Republic as a mortal menace to the Jewish state. Iran says it enriching uranium only for peaceful nuclear energy.
Kerry said Washington would confer closely with its Israeli ally about crafting a permanent Iran agreement after the six-month confidence-building period laid out by the Geneva deal under which Iran will curb sensitive aspects of its nuclear program in exchange for limited relief from sanctions.
"I can't emphasize enough that Israel's security in this negotiation is at the top of our agenda and the United States will do everything in its power to make certain that Iran's nuclear program, the program's weaponisation possibilities, is terminated," Kerry said.
GOING SLOW ON SANCTIONS
The Obama administration was warning any other country against "moving ahead of sanctions" in trading with Iran, Kerry said.
"The fundamental sanctions regime of oil and banking remains absolutely in place. It is not changed. And we will be stepping up our effort of enforcement through the Treasury Department and through the appropriate agencies of the United States," Kerry said.
Israel's fierce opposition about the Geneva deal have raised speculation - fuelled by regular public hints from Netanyahu - that it might carry out long-threatened unilateral strikes against Iran.
But while Israel is widely assumed to have the region's only nuclear arsenal, many independent analysts believe it lacks the conventional clout to deliver lasting damage to the distant, dispersed and well-defended Iranian facilities.
The Israelis are also unlikely to go it alone as their most important foreign partner is engaged in diplomacy with Tehran.
Hoping to stay Israel's hand, the Americans have invested heavily in its strategic defenses. Kerry said that during his visit he hoped to tour Palmahim air base, near Tel Aviv, where Israel's command-and-control centre for the Arrow ballistic missile interceptor and other systems is located.
"I want to see first-hand the remarkable ballistic missile defense technologies in place that our nation has spent over 20 years building with our friends here in Israel," he said.
"The advancement of these programs in recent years, I think, is a reflection of President Obama's and his administration's strong commitment, unwavering commitment to Israel's security."
© 2017 Reuters All rights reserved.
