President Barack Obama says he won't spell out specific boundaries Iran can't cross in its nuclear program before facing U.S. military action, CBN News reports. In an hour-long conversation Thursday with Israeli Prime Minister Benjamin Netanyahu, Obama refused Netanyahu's request to set limits on Iran and draw a "red line," such as the amount of near-weapons-grade uranium Iran can produce. But Obama did promise 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, senior fellow at the Washington Institute for Near East Policy, told the New York 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."