The Syrian government delegation chief at peace talks said on Tuesday it was too early to begin indirect discussions since he was still waiting for the U.N. special envoy to provide a list of the opposition’s negotiating team.

Staffan De Mistura announced on Monday the formal start of the negotiations. But Syrian government delegation chief Bashar al-Ja’afari said the U.N. envoy had now realised that conditions were not ripe for indirect “proximity talks”, with government and opposition delegations in separate rooms.

“The circumstances on the formalities are not yet ready. We are in the preparatory stage before the official launch of indirect negotiations,” Ja’afari told reporters after a 2-1/2 hour 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 finalised.” A U.N. source said De Mistura, trying to broker an end to a civil war that has killed 250,000 people and driven 10 million from their homes, had promised he would provide the opposition delegation list by Wednesday.

Ja’afari said that if the opposition “really cared” about the lives of Syrians it should condemn the killing of more than 60 people on Sunday by Islamic State suicide bombers at the country’s holiest Shi’ite Muslim shrine.

Representatives of the main opposition High Negotiation Committee (HNC) – which includes political and militant opponents of President Bashar al-Assad – have warned that they will not negotiate unless the government stops bombarding civilian areas, lifts blockades and releases detainees.

Asked whether Damascus was ready to discuss these issues, Ja’afari said all issues were a priority for the government, including terrorism and humanitarian matters. “Once the dialogue officially starts, we will start to deal with these issues,” he said, repeating that there should be no preconditions for talks.

Supported by Russian air strikes, Syrian government forces and their allies are advancing against rebels in several areas of the country’s west where the country’s main cities are located, and on Tuesday were threatening rebel supply lines into the northern city of Aleppo.

HNC spokesman Salim al-Muslat said the opposition was still undecided on whether to meet De Mistura as planned at 5 p.m (1600 GMT), and he accused Russia of endangering the process.

“It is clear from the current situation that the regime and its allies – in particular Russia – are determined to reject the U.N.’s efforts to implement international law,” he said.

“The regime and Russia’s actions gravely threaten the political process at this early stage.” He called on major powers to put pressure on Moscow.

“It seems nobody is helping us. Nobody is serious. We really trust our friends … but we need to see (it) – if they take one step then we will take 10. But let them do something.”