JERUSALEM — An Israeli official said Monday that Washington's refusal to issue an ultimatum to Iran over its nuclear program brings Tehran closer to producing an atomic bomb.

Israel has been pushing for the international community to give Iran "clear red lines" with regard to the disputed program, which Tehran insists is for peaceful purposes only. An Israeli official reiterated his country's position on Monday night, speaking on condition of anonymity because of the sensitivity of the issue.

"Without a clear red line Iran will not cease its race toward a nuclear weapon," he said.

Israeli leaders have been hinting at a possible military strike to stop Iran from acquiring an atomic weapon. The U.S. says sanctions and diplomacy should be given more time.

Israel sees a nuclear Iran as an existential threat, due to its arch foe's frequent calls for Israel's destruction, its missile program and support for violent groups such as Hamas and Hezbollah.

Speaking to reporters in Washington, State Department spokeswoman Victoria Nuland said "it is not useful to be ... setting deadlines one way or another" or to outline "red lines" for how far the U.S. can allow Iran's nuclear program to advance.

She repeated that President Barack Obama has stated unequivocally that the United States will not allow Iran to obtain a nuclear weapon, and that U.S. support for Israel's security is unwavering.

But she said she would not speak about ongoing discussions between the U.S. and Israel, calling such talk "not helpful for the diplomacy."