Condemning rampant war crimes in Syria's nearly five-year-old war, a report by a U.N. commission of inquiry said Monday that accountability for these horrors must be part of the peace process.

The report also took aim at world powers backing Syria's peace process for "paradoxically" seeking a settlement while feeding a recent escalation on the battleground.

A string of bomb attacks on Sunday near a Shiite shrine south of Damascus killed 120 people, in the deadliest attack since Syria's war erupted in 2011, a monitor said.

At least 90 civilians were among those killed when suicide attacks claimed by the Islamic State jihadist group ripped through the area of the Sayyida Zeinab shrine, the Syrian Observatory for Human Rights said.

Russia's foreign ministry said Monday that a string of suicide bombings in Syria at the weekend claimed by the Islamic State group were aimed at undermining the peace process.

"The atrocious crimes of extremists are aimed at scaring the peaceful population, subverting attempts to reach a long term political settlement to the Syrian crisis in the interests of all Syrians and efforts to end violence and bloodshed," it said in a statement.

U.S. Secretary of State John Kerry said Sunday that a provisional agreement had been reached with Russia on the terms of a ceasefire in Syria.

Kerry told reporters in the Jordanian capital Amman that he had spoken with Russian counterpart Sergei Lavrov again on Sunday on the terms of a ceasefire agreed by world powers earlier this month.

Saudi forces participating in any U.S.-led ground operation in Syria would focus on fighting the Islamic State group not President Bashar Assad, Saudi Arabia's foreign minister told AFP on Thursday.

In an interview in Riyadh, Adel al-Jubeir also said separate Saudi-led military operations in Yemen would continue until the country's government is fully restored to power and that the kingdom would not cut oil production despite falling prices.

Two Syrian mothers who crossed from Turkey to Greece on a refugee boat said Thursday that they were separated from their children during a Turkish coastguard operation to stem the flow of migrants.

The women told journalists their boat was intercepted mid-sea by the Turkish coastguard, who began transferring migrants to their patrol vessel to return them to Turkey, starting with the children -- when the handler of their boat started the engine and sped off towards the Greek coast.

Turkey will not allow the Syrian town of Azaz just across from the Turkish border to fall under the control of Syrian Kurdish fighters, Prime Minister Ahmet Davutoglu said on Monday.

"We will not let Azaz fall," Davutoglu was quoted as saying by the private NTV television on his plane en route to an official visit to Ukraine.

Russia must change its military targeting as it backs the Syrian regime, U.S. Secretary of State John Kerry said Saturday, as world powers seek a cessation of hostilities in the country within a week.

"To date, the vast majority of Russia's attacks have been against legitimate opposition groups," Kerry said of Moscow's air strikes in support of President Bashar al-Assad's forces. 

Representatives of 17 countries will meet in Geneva Friday afternoon for United Nations-hosted talks on how to ensure humanitarian access in war-ravaged Syria, a U.N. spokeswoman said.

"The humanitarian group will meet today at 4:00 pm (1500 GMT)," Khawla Mattar, a spokeswoman for U.N. Syria envoy Staffan de Mistura, told AFP in an email.

Russia's defense ministry on Thursday accused the United States of bombing the Syrian city of Aleppo after the Pentagon said Moscow's air strikes had destroyed two hospitals in the city.

Moscow furiously denied the U.S. claim, charging in return that Washington had sent ground-attack planes to bombard Aleppo, an allegation the U.S. said was a "fabrication".