After a meeting with British Prime Minister David Cameron, Obama spoke of "inherent limits" on the U.S. airstrike operation, and emphasized the importance of the Libyan people fighting for their own liberty.
"We will not relent until the people of Libya are protected and the shadow of tyranny is lifted," Obama told a gathering of the British Parliament on Wednesday afternoon. "Ultimately, freedom must be won by the people themselves, not imposed from without."
The remarks came on a day of political meetings for the president, in Europe to meet with Cameron and other allies at a pivotal time for their shared military goals.
As Obama pushes for a continued commitment in Afghanistan, some European leaders are more focused on ending the campaign in Libya -- with some officials suggesting that the U.S. should bring greater force to bear on the regime of Libyan leader Moammar Kadafi.
In a joint news conference after their one-on-one meeting in the morning, Cameron praised the U.S. work thus far, telling reporters that U.S. airstrikes have had a significant effect in Libya.
Addressing questions about whether the U.S. would commit greater resources, Obama reminded reporters that he has vowed not to send ground troops to Libya.
"Once you rule out ground forces," Obama said, "then there are going to be some inherent limitations to our airstrike operation."
The U.S. doesn’t have a "secret, super-effective" aircraft sitting unused in a warehouse somewhere, he said.
Even if the country did have that silver bullet, Obama made clear he might not use it.
"We will proceed with humility," he said, "and the knowledge that we cannot dictate outcomes abroad."