WASHINGTON - Defending his cautious approach to Syria, President Obama today said the U.S. has both a "moral obligation and a national security interest" in ending the bloodshed, but cautioned that he will not make any decisions about U.S. involvement based on the "perceived" use of chemical weapons.

"Understandably, there's a desire for easy answers," Obama said a White House press conference with South Korean President Park Geun-hye. "That's not the situation there, and my job is to constantly measure our very real and legitimate humanitarian and national security interests in Syria, but measuring those against my bottom line, which is, what's in the best interests of America's security, and making sure that I'm making decisions not based on a hope and a prayer but on hard-headed analysis in terms of what will actually make us safer and stabilize the region."

The Obama administration has found evidence that chemical weapons were used in Syria and continues to investigate how they were used, when they were used, and who used them.

"I don't make decisions based on 'perceived.' And I can't organize international coalitions around 'perceived.' We've tried that in the past, by the way, and it didn't work out well," he said, referring to the Iraq War. "So we want to make sure that, you know, we have the best analysis possible. We want to make sure that we are acting deliberately."

Obama has said repeatedly that the use of chemical weapons by the regime of President Bashar Assad would be a "game-changer" and that any additional steps will be taken based on information on the ground.

The president seemed to underscore his adherence to his "red line," pointing to the killing of Osama bin Laden and U.S. involvement in the overthrow of Libyan dictator Moammar Gadhafi as evidence that "we typically follow through on our commitments."

"I would just point out that there have been several instances during the course of my presidency where I said I was going to do something, and it ended up getting done," he said.