Prime Minister Benjamin Netanyahu on Friday said he is skeptical that Iran will agree to halt its nuclear program.
"I see no evidence whatsoever that Iran is ready to end its nuclear program," he said just days ahead of a crucial round of nuclear talks with Tehran.
The P5+1 – the five permanent members of the UN Security Council plus Germany – are set for a May 23 meeting with Iran in Baghdad.
Speaking in Prague, Netanyahu called it "the paramount issue of our time."
Netanyahu did not present any ultimatums, but Israeli officials have said time is running out to avoid military action.
This marks the third time in recent months Netanyahu has said he does not believe Western sanctions will prove effective in halting Iran's nuclear program.
His government maintains a nuclear weapon in the hands of Iran would threaten the Jewish state's survival.
Israel is not alone in believing Tehran is pursuing nuclear research with military applications – or considering a military strike in Iran's nuclear sites.
US ambassador to Israel Daniel Shapiro this week indicated Iran now had a very short "window" in which to agree to a diplomatic solution.
"It would be preferable to resolve this diplomatically and through the use of pressure than the use of military force," Shapiro said during a speech in Tel Aviv.
"But that doesn't mean that option is not fully available - not just available, but it's ready. The necessary planning has been done to ensure that it's ready."
While US officials have made tangential references to a "military options" vis-a-vis Iran, none have done so in such forthright terms to date.
International Atomic Energy Agency officials are pressing Iran to address concerns spelled out in an extensive IAEA report released in November 2011.
The report alleges that at least until 2003, and probably since then, Tehran has engaged in nuclear activities of a decidedly military nature.
They also want access to the Parchin military base near Tehran where the IAEA report – which cited foreign intelligence, its own sources, and Iranian information – said Iran had conducted high-explosives tests in a specially designed chamber.
Two previous trips to Tehran in January and February by the IAEA resulted in Iran denying inspectors access to suspected nuclear sites.
Iran, as a signatory to the Nuclear Non-Proliferation Treaty, is obligated to allow the UN watchdog access to its site for inspections to ensure it is complying with the treaty.
IAEA chief Yukiya Amano said recently that access to Parchin was a "priority" and that "activities" spotted by satellite there "makes us believe that going there sooner is better than later."
In March, Amano also charged Iran with a systemic attempt to cover up nuclear activity of a military nature saying, "Iran is not telling us everything."
Western nations have accused Iran of removing evidence from Parchin and other sites - and Tehran's Gulf Arab rivals have also charged Iran is seeking nuclear weapons.