Renewed international efforts to negotiate curbs on Iran’s disputed nuclear programme have backfired by giving it more time to work on building a bomb, Israeli Prime Minister Benjamin Netanyahu said on Sunday.

His remarks on the inconclusive Feb. 26-27 meeting between Iran and six world powers signalled impatience by Israel, which has threatened to launch preemptive war on its arch-foe, possibly in the coming months, if it deems diplomacy a dead end.

Senior US diplomat Wendy Sherman flew in to brief Israel about the Kazakh-hosted talks, in which Tehran, which denies seeking nuclear arms, was offered modest relief from sanctions in return for halting mid-level uranium enrichmentThere was no breakthrough. The sides will reconvene in Almaty on April 5-6 after holding technical talks in Istanbul.

My impression from these talks is that the only thing that is gained from them is a buying of time, and through this time-buying Iran intends to continue enriching nuclear material for an atomic bomb and is indeed getting closer to this goal,” Netanyahu told his cabinet in remarks aired by Israeli media.

Extrapolating from UN reports on Iran’s enrichment of uranium to 20 percent fissile purity, a short technical step from weapons-grade, Netanyahu has set a mid-2013 “red line” for denying the Islamic republic the fuel needed for a first bomb.

The prospect of unilateral Israeli strikes, and the likely wide-ranging reprisals by Iran and its regional allies, worries Washington, which wants to pursue diplomacy as it winds down costly military commitments abroad.