"This topic will not be covered in the final text of the document," the source said.
According to the source, the issue of the Russian operations in Syria has caused heated discussion among the participants. The parties have failed to reach a consensus on this issue, the source said.
"We need time to assess what impact this step on the part of Moscow will have, and to develop a common response to this issue," the source added.
The Astana-2 Syrian opposition conference is held on October 2-4. The previous conference in May saw Syrian opposition groups sign off on a document calling for the withdrawal of all foreign mercenaries from Syria and stressing the necessity to form a unified front to counter terrorism.
Syrian opposition groups are discussing the transition of power in their home country, the fight against terrorism and the long-standing civil war in the country.
On Thursday, Syrian Ambassador to Russia Riad Haddad confirmed that Syrian Army strikes, supported by the Russian Air Force, were carried out against armed terrorist organizations and not political opposition factions.