President Obama said Sunday that the United States will not hesitate to attack Iran with military force to prevent it from acquiring a nuclear weapon, but he cautioned that "too much loose talk of war" recently has only helped Tehran and driven up the price of oil.

Speaking to a powerful pro-Israel lobbying group, Obama appealed to Israel for more time to let sanctions further isolate Iran. He sought to halt a drumbeat to war with Iran and hold off a unilateral Israeli strike against Iran's nuclear facilities.

"For the sake of Israel's security, America's security and the peace and security of the world, now is not the time for bluster," Obama told thousands at the annual American-Israel Public Affairs Committee's policy conference. "Now is the time to let our increased pressure sink in, and to sustain the broad international coalition that we have built."

Quoting President Theodore Roosevelt, Obama said he would "speak softly, but carry a big stick" and warned Iran not to test U.S. resolve.