A string of suicide bombings near a shrine outside Syria's capital and in Homs claimed by Daesh killed more than 150 people Sunday, as Washington and Moscow worked to secure a ceasefire.
Daesh said it was behind the carnage.
US Secretary of State John Kerry said a provisional deal had been reached on the terms of a truce in Syria's brutal five-year conflict, only for the bloodshed to intensify on the ground.
Near Damascus, a car bombing followed by two consecutive suicide attacks ripped through the area of the shrine of Sayyida Zeinab and killed 96 people according to The Syrian Observatory for Human Rights.
Syria's official news agency Sana, quoting a police source, said 178 people, including children, were among the wounded.
A January attack in the same area - also claimed by Daesh - killed 70 people.
The Observatory also reported that two car bombs killed at least 59 people and wounded dozens in the pro-regime district of Al-Zahraa in the central city of Homs.
Daesh said online that two suicide bombers struck in Sayyida Zeinab and two others drove explosive-packed cars into crowds in Homs.
UN special envoy for Syria Staffan de Mistura "strongly condemns" the attacks, his spokesperson said in a statement.
State television footage from Homs showed emergency workers carrying a charred body on a stretcher past devastated shops and mangled cars and minibuses.