"We will strive to join the political process," Salem al-Meslet said after a first formal meeting between UN envoy Staffan de Mistura and the High Negotiations Committee in Geneva.
"We came here to discuss with the special envoy UN resolution 2254 lifting the sieges and stopping the crimes done by Russian air strikes in Syria, and I believe we received positive messages," he said.
The opposition delegation has insisted it will not formally join peace talks until those humanitarian demands are met.
He also accused the Russian government -- a stalwart ally of the regime in Damascus -- of helping to turn Syrian President Bashar al-Assad into a "new Hitler."
"(The) Russian regime will create a new Hitler. We are suffering from a Hitler in Syria," Meslet told journalists.
More than 260,000 people have been killed in Syria's nearly five-year war, which has drawn in world powers including Gulf states, Russia, and the United States.