Israeli Prime Minister Benjamin Netanyahu has been meeting with world leaders for the past few months, encouraging them to take tough action to stop Iran's pursuit of nuclear weapons.

Most recently Netanyahu returned from meetings with Russian leaders President Dmitry Medvedev and Prime Minister Vladimir Putin.

"I quoted to each of them the words of Hillel the Elder from 2,000 years ago. He said 'If not now, when,'" Netanyahu told the Jerusalem Conference shortly after his return. "If crippling sanctions are not imposed on Iran now, when will they be? When? In a year? Two? Three years? When will they impose those sanctions? If not now, when? I say now."

"Russia understands very well the problem posed by a nuclear Iran," Netanyahu added. "The most important thing now is that there is a general interest ... that Iran not become a nuclear power."

The prime minister said only forceful sanctions and not superficial ones will have an impact.

Iran has already defied three sets of U.N sanctions. Though Russia has generally resisted new sanctions, the country has shown increasing frustration over the past week with Iran's plan for uranium enrichment.