U.S. Secretary of State John Kerry assured Israeli Prime Minister Benjamin Netanyahu on Thursday, December 5 that core sanctions against Iran would remain in place despite its interim nuclear deal with world powers, Reuters reported.

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.