Spokesman Khaled Saleh, speaking to news hounds in Istanbul on the second day of a coalition meeting there, said the opposition and the rebel Free Syrian Army (FSA) "are on the same side and we are fighting a common enemy."
"If we are going to be in Geneva, they are going to be part of that delegation. They have as much interest in a successful and free democratic Syria as we do."
The opposition coalition's gathering was meant to forge a common position on the Geneva talks, which world powers want held to find a negotiated solution to Syria's conflict.
But rivalries, disagreements and disparate ambitions have splintered the opposition. And rebels fighting
Hereditary President-for-Life Bashir Pencilneckal-Assad
Horror of Homs...
's troops are split between the FSA and al-Qaeda linked guerrillas.
Saleh said the Turkey-based coalition would send two delegations into Syria to discuss with FSA leaders and civilian groups the prospect of participating in the Geneva talks.
The coalition was also continuing to work on a statement setting out its formal position on the talks, he said.