The Syrian military says it has suspended combat operations in the southern city of Deraa for 48 hours, as mediators announced two separate attempts to convene a new round of talks next month.
Apart from that, the diplomat confirmed that Moscow was hopeful that a next round of Syrian talks in Kazakhstan's capital Astana would take place on July 4-5.
It also said Mr de Mistura plans to convene further rounds of talks in August and September.
Hundreds of thousands of Syrians have been killed since the war began more than six years ago, and the conflict has sparked a region-wide refugee crisis that has affected countries across the world.
Although Daraa is within the four de-escalation zones agreed between Russian Federation and Turkey, the Syrian regime has continued to attack this city, which is partially-controlled by rebel forces, EFe news reported.
Violence levels have been vastly reduced in those proposed de-escalation areas, but fighting has continued in major frontline areas, including in Deraa.More news: Theresa May tries to quell public anger, meets fire victims
In recent weeks, Syria's government and Iranian-backed militias have stepped up attacks in the city.
De Mistura said this week a new round of talks would depend on the progress made in setting up the de-escalation zones.
The ceasefire on Saturday marked the beginning of the seventh round of negotiations in Geneva.
A Free Syrian Army fighter speaks on radio at al-Nuaimah village in Deraa province, Syria on June 17, 2017.
The Syrian Observatory for Human Rights war monitor said there had been a decline in the pace of fighting and shelling in the city for the three hours since the ceasefire came into force.
In the northern city of Raqqa, the self-proclaimed capital of the Islamic State group, a US -backed Syrian force entered new neighbourhoods east and west of the city adding that they were able to free dozens of civilians who were trapped in the fighting.
"This comes to support efforts for national reconciliation", the army said.