President Obama is calling the possible use of chemical weapons in Syria a "big event of grave concern."
But the president went on to say he would seek international support before taking any large-scale action.
"If the U.S. goes in and attacks another country without a U.N. mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it [and] do we have the coalition to make it work," Obama said in an interview with CNN. "Those are considerations that we have to take into account."
He said the United States is still looking for conclusive evidence that Syria did use chemical weapons this week.
A U.N. team is in Syria to investigate earlier allegations of chemical weapons use. The United States has asked Syria to let them investigate Wednesday's attack, but said "We don't expect cooperation, given their past history."
The president has come under fierce criticism for his lack of action in Syria.
Some critics, like Arizona Sen. John McCain, say America's credibility has been damaged because Obama hasn't taken more forceful action to stop the violence. The death toll in the two-year civil has topped 100,000.
But the president said the United Statse should not get involved everywhere immediately.
More than half of the nearly 2 million refugees from the Syrian civil war are children, most less than 11 years old.
The United Nations reports the number of registered child refugees topped the 1 million mark this week, with some 740,000 under the age of 11.
About 7,000 children have died in the fighting between Syrian rebels and the government.