The United States, Russia and Jordan reached a ceasefire and "de-escalation agreement" this week with the aim of paving the way for a broader, more robust truce.
The announcement came after a meeting between US President Donald Trump and Russian President Vladimir Putin at the G20 summit of major economies in Germany, Reuters reported.
Several ceasefires have crumbled since the onset of the conflict and it was not clear how much the combatants - Syrian government forces and the main rebels in the southwest - were committed to this latest effort.
With the help of Russian air power, Syrian President Bashar al-Assad's government has put rebels on the back foot over the last year.
Earlier talks between the US and Russia about a "de-escalation zone" in southwest Syria covered Deraa province on the border with Jordan and Quneitra, which borders the Israeli-occupied Golan Heights.
A senior State Department official involved in the talks said further discussions would be necessary to decide crucial aspects of the agreement, including who will monitor its enforcement.
Russian Foreign Minister Sergei Lavrov said the deal includes "securing humanitarian access and setting up contacts between the opposition in the region and a monitoring center that is being established in Jordan's capital."