His comments came as the regime launched air strikes for the first time against a Palestinian refugee camp in Damascus, drawing condemnation from both Palestinian president Mahmud Abbas and the Hamas rulers of Gaza.
"No opposition can end the battle militarily, just as the security forces and army cannot achieve a decisive conclusion," Sharaa told the pro-Damascus Lebanese daily Al-Akhbar on Sunday.
"Every day that passes, we are moving further away from a military or political solution, " said Shara, who is the most prominent Sunni Muslim in the Alawite minority-dominated regime of President Bashar al-Assad.
"We must position ourselves to defend Syria's existence. We are not in a battle for an individual or a regime.
"The various opposition forces, whether armed or civilian, or linked to foreign powers, cannot claim they are the sole legitimate representatives of the Syrian people," he added, referring to the decision of Arab and Western governments last week to recognise the armed opposition.