The next round of intra-Syrian talks in Geneva will take place in early September, de Mistura told reporters.
"The next round will take place in early September. I have asked the parties to have clear substantial issues on all the 4 baskets," de Mistura said.
The four baskets are anti-terrorism, governance, constitution and elections.
He also said he has got no indication so far from the Syrian government delegation on their readiness to address the issue of political transition issue.
"No, i don't have any indication," de Mistura said, asked whether he has been given any indication from the government delegation on their readiness to address political transition at the Geneva talks.
De Mistura said he would be interested in taking part in the next international meeting on Syria in the Kazakh capital of Astana.
"I would be very much interested in it, but the invitations have not been sent so far," de Mistura told Sputnik, answering the question whether he plans to come to the next Astana meeting.
The negotiations on the Syrian crisis settlement take place on two parallel platforms: UN-mediated Geneva talks, and Astana talks that are brokered by Russia, Turkey and Iran. The latest Astana negotiations were held on July 4-5.
The high-level international meeting on Syria in Astana will most likely take place in late August, a source close to the negotiations process told Sputnik this week.