President Barack Obama made the case on Wednesday for a limited military strike against Syria to deter the future use of chemical weapons, but added he had not made a decision yet on whether to take action.
Obama's administration has spent the past week discussing how to respond to an attack in the suburbs of Damascus that killed hundreds of people, an attack that the president said could only have been made by the Syrian government.
A senior U.S. official has said strikes could last several days and would involve other country's armed forces. Western armies are expected to wait until U.N. investigators leave the country in several days.
Obama said a "tailored, limited" strike, not a protracted engagement like Iraq, could be enough to send a strong message that the use of chemical weapons cannot be tolerated.
"If we are saying in a clear and decisive but very limited way, we send a shot across the bow saying, 'Stop doing this,' this can have a positive impact on our national security over the long term," he told "PBS Newshour" in a televised interview.
Obama said U.S. officials had concluded the Syrian government was responsible for the attacks, and did not believe the Syrian opposition had a role in them.
U.S. national interests could be at risk if Syrian chemical weapons fall into the wrong hands, Obama said.
"We want to make sure that they are not loose in a way that ultimately, could affect our security," he said.
Reporting by Jeff Mason, Roberta Rampton and Mark Felsenthal; Editing by Peter Cooney