A former Israeli spymaster on Thursday cautioned Iran not to dismiss Israel's talk about possibly attacking Iranian nuclear facilities.

The next 12 weeks will be "very critical" to Israel's decision on whether to strike, Ephraim Halevy said. That time frame coincides with the run-up to the U.S. presidential election.

"If I were an Iranian, I would be very worried about the Israeli talk about a possible attack, because Israel's threats sound serious and credible to me," Halevy, who left the Mossad a decade ago, told Israel Radio.

Iran contends its nuclear program is peaceful and designed to mostly produce energy. But Israel thinks Tehran's uranium enrichment activities are a cover for bomb-making, and like the U.S. has said it would not tolerate a nuclear Iran.

Israel considers Tehran to be its most fearsome enemy and does not lightly take multiple references by Iranian officials to the Jewish state's destruction. It says nuclear talks with Iran and tough sanctions against it have been ineffective — an apparent swipe at U.S. policy.

American officials oppose a near-term military strike on Iran and have pressed Israel to give diplomacy and sanctions a chance to work. A strike before U.S. elections three months from now would likely drive up oil prices and drag the U.S. into another domestically unpopular Mideast conflict during the election campaign

Prime Minister Benjamin Netanyahu said earlier this week that Israel hasn't decided whether to strike Iran. But before meeting with U.S. Defense Secretary Leon Panetta on Wednesday, Netanyahu sounded impatient with U.S. efforts to curb Iran's nuclear program, saying Washington's strategy of diplomacy and sanctions was perilously close to failure.

"Right now the Iranian regime believes that the international community does not have the will to stop its nuclear program," Netanyahu said. "This must change, and it must change quickly because time to resolve this issue peacefully is running out."