President Obama was interviewed by CNN on Friday.
President Barack Obama says the United States cannot attack Syria without a UN mandate for the allegations that the Syrian government used chemical weapons.
"If the US goes in and attacks another country without a UN mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it. Do we have the coalition to make it work? And, you know, those are considerations that we have to take into account," he said in an interview with CNN on Friday.
The remark was made when asked it has been one year since Obama said the use of chemical weapons in Syria would cross a "red line" and prompt a tough US response.
Syria's foreign-backed opposition claimed that more than 1,000 people were killed in a government chemical attack on militant strongholds.
A team sent by the United Nations is set to investigate the latest claim of chemical weapons use outside Damascus.
UN Secretary General Ban Ki-moon on Thursday asked Syria to allow UN inspectors to investigate "without delay" the alleged chemical attack.
A top Pentagon official also said on Friday the US military has updated its options for a military strike, adding that target lists for possible airstrikes have been updated.
The planning also included updates on the potential use of cruise missiles, which would not require fighter pilots to enter Syrian airspace, the unnamed official said.
President Obama also pointed to the high costs of other recent American engagements, saying, "We're still spending tens of billions of dollars in Afghanistan.”
"Sometimes what we've seen is that folks will call for immediate action, jumping into stuff, that does not turn out well, gets us mired in very difficult situations, can result in us being drawn into very expensive, difficult, costly interventions that actually breed more resentment in the region," Obama said.