President Obama, invoking the massacres in Rwanda and the Balkans, said Friday that the international community has an obligation to prevent a "repeat" of those tragedies in Libya -- as Muammar al-Qaddafi makes gains against the rebels fighting to overthrow him.

But amid concerns that the administration may be exhausting its diplomatic options, the president stressed that the U.S. and its allies are moving with unprecedented determination to isolate the Libyan leader. He said he would not take any option, including a military response, off the table, and defended the administration's approach.

"We are slowly tightening the noose on Qaddafi," he said.

Obama said the ultimate goal is for Qaddafi to step down. He seemed to push back on his chief intelligence officer's assessment that the regime will likely "prevail."

"He was making a hard-headed assessment about military capability," Obama said of Director of National Intelligence James Clapper's remarks the day before, which stirred controversy on Capitol Hill. "I don't think anybody disputes that Qaddafi has more firepower than the opposition."

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But Obama said Clapper was not stating "policy," something he stressed is determined by the president. That policy, Obama said, is that Qaddafi is on "the wrong side of history" and must step down.

To achieve that, Obama said NATO will meet Tuesday to consider a no-fly zone; the U.S. is gauging support among Arab and African nations for further action; Secretary of State Hillary Clinton will soon meet with opposition leaders; and the administration will assign a special representative to deal with the opposition and determine ways to help their cause.

"I have not taken any options off the table at this point," Obama said.

The president said it is in the U.S. interest for Qaddafi to leave, though he also stressed that the United States will be able to buffer itself against any disruption in the oil supply. He said he's "prepared" to tap into the U.S. oil reserve to alleviate rising gas prices if necessary.

Still, some have expressed concern that Qaddafi will continue to make gains, as Clapper warned, unless western forces move beyond diplomatic options soon.

Bill Richardson, former United Nations ambassador and governor of New Mexico, told Fox News that a NATO-backed no-fly zone over Libya "probably needs to happen," and suggested western allies look at options for airlifting supplies and weapons to the rebels.

"It has reached a point where this is a civil war," Richardson said. "I think there is justification on human rights grounds for a limited military operation."

Though nobody prominent is calling for ground forces to be sent in, calls for a no-fly zone or other military options have been countered with warnings that the United States risks getting bogged down in a long-term conflict when U.S. forces are already stretched -- and could inadvertently fuel support for Qaddafi.

"We can stand on the sidelines and hope and pray for the best; we can get so involved that we are accused of interfering, going after oil, trying to occupy another Islamic country," Clinton said. "Or we can try to do what we are doing, which is, be smart about how we offer assistance, how we respond, how we bring the international community along. And that's the toughest of the options, but that's what we're trying to do."

Rep. Ron Paul, R-Texas, one of Congress' toughest critics of U.S. intervention abroad, told Fox News "there's no way we can afford" getting involved militarily in Libya. He said he would introduce a resolution next week to restrict Obama from approving any military action without congressional approval.

Defense Secretary Robert Gates, while keeping the option of a no-fly zone on the table, has like Clinton urged caution against moving ahead with a military response too quickly.

National Security Adviser Tom Donilon pushed back on Clapper's pessimism Thursday.

"Things in Libya in particular right now need to be looked at not through a static but a dynamic, and not through a uni-dimensional, but a multidimensional lens," he said. "And if you look at it in that way, beyond a narrow view, on just kind of numbers of weapons and things like that, you get a very different picture. The lost legitimacy matters. The isolation of the region matters. Denying the regime resources matters. And this can affect the sustainability of their efforts over time."