At least 140 people have been killed in serial bomb blasts in Syrian cities of Homs and Damascus in a day of carnage claimed by the Islamic state.
Monitoring groups also said attacks by the government troops killed at least 50 Islamic State fighters in the northern city of Aleppo.
Syrian state media said 83 people were killed in four blasts in southern Damascus suburb of Sayyida Zeinab, while a monitoring group said a double car bombing killed 57 people, including several civilians, in Homs.
The deadly attacks on Sunday came even as US Secretary of State John Kerry said he and his Russian counterpart Sergei Lavrov reached a "provisional agreement" with Russia on a partial ceasefire in Syria.
In both the attacks, the Sunni Muslim Isis militia targeted areas dominated by the Shia community. At least four bombs went off in Damascus' Sayyida Zeinab area, where one of Syria's holiest Shia Muslim shrines is located.
Syria's state-run news agency Sana said the blasts left 178 people wounded.
The blasts in Homs targeted a district dominated by President Bashar al-Assad's Alawite sect.
According to the Syrian Observatory of Human Rights, the car bombings in Homs, which left more than 100 wounded, were among the deadliest in the city in five years of conflict.
Meanwhile, the Observatory said a government offensive backed up by Russian air strikes killed at least 50 Islamic State fighters the northern city of Aleppo in the past 24 hours.
The provisional truce agreement between Kerry an Lavrov followed an expression of willingness by both Assad and the opposition fighters for enforcing a conditional halt on the fighting.
"We have reached a provisional agreement in principle on the terms of a cessation of hostilities that could begin in the coming days," Kerry said.
"The modalities for a cessation of hostilities are now being completed. In fact, we are closer to a ceasefire today than we have been," he said in Jordan.
Russia's foreign ministry also confirmed Lavrov and Kerry conducted talks about the conditions for a ceasefire, Reuters reported.