The president's declaration was in line with the apparent prevailing sentiment in Washington. Even one of Obama's chief antagonists on Syria, Sen. John McCain, R- Ariz., has said he does not advocate sending ground troops, arguing that would be "the worst thing the United States could do right now."
Obama also said he had consulted with Mideast leaders who want to see Syrian President Bashar Assad's departure and agree with his assessment that the U.S. shouldn't send ground forces. After long wars in Afghanistan and Iraq, another U.S. intervention in the region could further inflame anti-American sentiment.
Obama, who was meeting with Central American leaders in Costa Rica, was asked what the United States would do if its investigations find firmer evidence of Syrian use of chemical weapons. He repeated his earlier assertion that it would be a "game-changer."
"We will stay on this," Obama said. The United States has sent humanitarian aid to the Syrian rebels, but not arms. The two-year civil war that has left an estimated 70,000 people dead and hundreds of thousands of refugees.
On Thursday, Defense Secretary Chuck Hagel said the Obama administration is rethinking its opposition to arming the rebels. Hagel said that the U.S. was consulting with allies and that and he personally hadn't decided whether it would be a wise move. Sending arms is considered risky partly because of fears that some would end up in the hands of al-Qaida-linked fighters and might someday be used against the United States.
Obama said the U.S. already is putting pressure on the Syrian government, including through humanitarian aid to the opposition. If systematic use of chemical weapons by Assad's forces were confirmed, he said, the United States would present that evidence to the international community.
"When it comes to using chemical weapons, the entire world should be concerned," he said.
He also stressed the importance of moving cautiously. The Syria question comes as the U.S. is leaving Afghanistan after more than a decade of war there, most of it fought as the nation was also at war in Iraq.
"When we rush into things, when we leap before we look, not only do we pay a price but oftentimes we see unintended consequences on the ground," Obama said. "It's important for us to do it right."
The administration announced last week that it believes Assad has used chemical weapons but said the intelligence wasn't clear enough to be certain that the regime has crossed a "red line" of definite chemical weapons use that he said would have "enormous consequences" for Assad's government.
Obama said Friday it's not yet clear when, where or how the weapons might have been used.