Bashar al-Jaafari said the U.N. envoy had now realised that conditions were not ripe for indirect "proximity talks".
"The circumstances on the formalities are not yet ready. We are in the preparatory stage before the official launch of indirect negotiations," Jaafari told reporters after a meeting with de Mistura.
"To prepare the official launch we have to have the presence of the two delegations, but on the other side the delegation has not been finalized," he said.
A U.N. source said de Mistura had promised he would provide the opposition delegation list by Wednesday.
Representatives of the opposition High Negotiation Committee (HNC) have warned that they will not negotiate unless the Assad regime stops bombarding civilian areas, lifts blockades and releases detainees.
Asked whether the Assad regime was ready to discuss these issues, Jaafari said all issues were a priority, including terrorism and humanitarian issues.
"Once the dialogue officially starts, we will start to deal with these issues," he said, repeating that there should be no preconditions for talks.