"We want a comprehensive ceasefire … So that the truce will cover all Syria and not just one region," Berri said.
According to the FSA chief of staff, the Syrian government will have to implement the ceasefire if the latter is reached by Moscow and Washington.
"Damascus will try to avoid approval of the ceasefire by any means … However, if the regime feels that Russia and the United States want to secure this ceasefire, then it will be implemented [by the Syrian government]," Berri noted.
Earlier in the day, UN Secretary-General's spokesman Stephane Dujarric said that the agreement on deescalation zones represents a significant step toward diffusing violence and increasing humanitarian access in Syria.
Immediately after the meeting between Russian President Vladimir Putin and his counterpart Donald Trump on Friday, Lavrov said that the experts from Russia, the United States and Jordan had agreed on a memorandum on the establishment of a deescalation zone. It covers Daraa, Quneitra and As-Suwayda provinces in southwestern Syria.