Iran, Russia and Syria on Thursday also rejected "all desperate attempts" by foreign-backed militant groups to undermine the sovereignty of the Syrian nation, Syria's official news agency SANA reported.
Syrian Ambassador to the United Nations Bashar al-Ja'afari called on all foreign forces operating without the permission of Damascus to leave the Arab country.
He also accused the US, Britain, France and Turkey of illegally dispatching troops to Syria and occupying some parts of the country.
In a declaration, the participants in the Astana talks also strongly denounced militant groups for firing shells filled with chlorine gas at Syria’s northern city of Aleppo this week.
The chemical attack was launched from an area in the Idlib de-escalation zone which is controlled by the Jabhat Fateh al-Sham, formerly known as Nusra Front.
In the past, the United States and its allies have used chemical attacks as a pretext to carry out missile strikes against Syria.
The 11th round of talks began Wednesday, with the participation of representatives from the Damascus government and opposition as well as the three guarantor states of the Astana peace process.
The discussions mainly focused on the situation in the de-escalation zone set up in Idlib Province and the creation of a constitutional committee in the war-torn country.
The 10th round of talks within the Astana format took place in the Russian Black Sea resort of Sochi on July 30-31.
The Astana talks have so far resulted in the return of a succession of militant bastions to the government fold, the establishment of safe zones across Syria and the movement of civilians to those regions.