Israel had a critical role in stopping a deal with Iran on reining in its nuclear program from going ahead last month, Israeli Prime Minister Benjamin Netanyahu said Sunday.

The deal would have "effectively left Iran as a threshold nuclear power," he told a Washington think-tank in a recorded speech.

"Even though Israel isn't part of the P5+1 our voice and our concerns played a critical role in preventing a bad deal."

The global powers known as the P5+1 who are leading efforts to stop Iran from developing a nuclear weapon have extended their talks until June 30, after they failed to meet the November 24 deadline for a deal.

Calling it the most "vital national security challenge we face," Israel and its allies "must use the time available to increase the pressure on Iran to dismantle is nuclear weapons capability," Netanyahu said.

Israel has publicly criticized US-led efforts to reach a deal to rein in Iran's suspect nuclear program, under which the Islamic republic would freeze much of its uranium enrichment program in return for sanctions relief.

Israeli officials have repeatedly warned that the administration of President Barack Obama is being fooled by the new, more moderate face of the Iranian leadership.

They say Iran will pay lip-service to any deal, pocketing billions in much needed cash-reserves while covertly still trying to develop an atomic bomb.

But addressing the Saban forum after the Israeli prime minister, US Secretary of State John Kerry insisted once again that the US administration would not allow Iran to obtain a nuclear bomb.

"While we may disagree on tactics from time to time, when it comes to the core strategic goal -- no nuclear weapon -- there is not an inch of daylight between the United States and Israel," Kerry said.

Iran has denied that it has been trying to develop an atomic weapon under the guise of its civilian nuclear energy program.

But Kerry reiterated that "systematically over many years Iran did not address the world's concerns about an illicit nuclear program."

He said a "verified, negotiated agreement" was the best way to "resolve the international community's legitimate concerns" as well as proving that Iran's "nuclear program is peaceful."

Despite the extended deadline, Kerry insisted the hope was now to wrap up the negotiations within the next three to four months.

"We have no intention of negotiating forever. And absent measurable progress, who knows how much longer this could go on," Kerry said.

The Obama administration is seeking to persuade Congress from adopting new sanctions against Iran in this interim period, arguing that it could scupper the entire delicate negotiating process.

"In recent weeks, we have seen new ideas surface, flexibility emerge, that could, I repeat could help resolve some issues, that had been intractable," Kerry said.