"We're not just going to walk away right now until the Geneva Process has traction," he told reporters.
"You need to do something about this mess now, not just fight the military part of it and then say good luck on the rest."
The former marine general added that the coalition's goal had always been to fight IS while finding a diplomatic solution to end the Syrian civil war.
"We are going to make sure we set the conditions for a diplomatic solution," he said.
His comments come after the US and Russia issued a joint statement Saturday saying there was "no military solution" to the Syrian conflict.
"The presidents affirmed their commitment to Syria's sovereignty, unity, independence, territorial integrity and non-sectarian character," it said, while calling on all parties to participate in UN-led talks in Geneva.
A new round of negotiations is scheduled to take place from November 28, a process headed by the UN special envoy on Syria, Staffan de Mistura.
Seven previous sessions between the Syrian regime and the opposition failed to overcome the main obstacle -- the fate of President Bashar al-Assad.
More than 330,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.
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