"Keep in mind that it's very hard to imagine that (the Syrian) civil war dying down if in fact Assad is still in power," Obama told the Spanish-language network Telemundo. (Agencies)
Obama has drawn some criticism for the deal to eliminate Syria's chemical weapons the United States negotiated with Russia, Syria's ally, because it does not directly punish Assad.
Obama said it is still his goal to "transition him out of power" in a way that protects Syria's religious minorities and ensures Islamist extremists are not gaining ground inside the country, where more than 100,000 people have been killed in a 30 months long civil war.
"But you know, we're going to take this one step at a time. The first step right now is to make sure we can deal with the chemical weapons issue," said Obama.
Afterward, he said, the next step will be to engage all the parties involved in the Syrian crisis and countries that have been supportive of Syria like Russia and say, "We need to bring an end to this."
UN investigators said on Monday that sarin gas killed hundreds of civilians in an August 21 attack on the suburbs of Damascus.
The chemical weapons deal sealed by US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov has drawn fire from critics who worry there is no strong enforcement mechanism to make certain Syria carries out its promises to give up these weapons.
"Keep in mind that it's very hard to imagine that (the Syrian) civil war dying down if in fact Assad is still in power," Obama told the Spanish-language network Telemundo.