President Obama said he won't spell out specific boundaries Iran can't cross in its nuclear program before facing U.S. military action.

The New York Times reported Thursday that the president refused Israeli Prime Minister Benjamin Netanyahu's request to set limits on Iran.

Netanyahu suggested President Obama draw a "red line," such as the amount of near-weapons-grade uranium Iran can produce.

In an hour-long conversation with Netanyahu, the president refused to draw such a line. But he did promise that the U.S. would not allow Iran to produce a nuclear weapon.

"The Israelis are worried that once Iran accumulates a bomb's worth of 20 percent-enriched uranium, it's an easy dash to get weapons-grade nuclear fuel," David Makovsky, a senior fellow at the Washington Institute for Near East Policy, was quoted by the Times.

"Before they decide they're on their own, I think they want to know that they and Washington see eye-to-eye that this is a red line that cannot be passed," he said.