Russia's foreign ministry condemned the "atrocious crimes of extremists".
Sunday's attacks hit the Shia shrine of Sayyida Zeinab, south of Syria's capital Damascus, and the city of Homs.
So-called Islamic State (IS) said it carried out the attacks. Both targeted areas dominated by Islamic minorities reviled by IS.
Four blasts in Sayyida Zeinab killed at least 83 people, according to state media. A monitoring group reported that 57 people, mainly civilians, were killed in a double car bombing in Homs.
The UK-based activist group Syrian Observatory for Human Rights (SOHR) put the toll from the Damascus attacks at 120 and said they were among the deadliest to occur during the whole of Syria's civil war.
SOHR also reported on Monday that heavy fighting had cut off the government's only supply route to the northern city of Aleppo.
IS and other Islamist militia had cut the road between Aleppo and the town of Khanasser to the south-east, it said.
More than 250,000 Syrians have been killed in the conflict.
Some 11 million others have been forced from their homes, of whom four million have fled abroad - including growing numbers who are making the dangerous journey to Europe.
History of the conflict - how the civil war has spread
Maps of the conflict - the shifting territorial gains
The Sayyida Zeinab district is the location of Syria's holiest Shia Muslim shrine, said to contain the grave of the Prophet Muhammad's granddaughter.
The district was hit by suicide attacks last month that left 71 people dead and which IS fighters also said they had carried out.
On Sunday US Secretary of State John Kerry said a "provisional agreement" had been reached with Russia on a partial truce.
However he admitted issues remained to be resolved and said he did not expect any immediate change on the ground.
Earlier this month, world powers involved in the crisis in Syria agreed to seek a "cessation of hostilities", but the Friday deadline came and went.
In Homs, the blasts happened in a predominantly Alawite district, the sect to which President Bashar al-Assad belongs.
One of the early centres of the uprising against President Assad, Homs was once dubbed the "capital of the revolution".
But rebels left the city late last year under a ceasefire deal, leaving the city in government hands.
The latest blasts came as President Bashar al-Assad told reporters Syrian refugees should not be scared of returning home.
Mr Assad, who has long been accused of persecuting his own people, said ordinary Syrians who had fled the conflict due to the "standard of living that has been deteriorating drastically" could go back without fear of action by the government.

The man, who has not yet been identified, was last seen alive at 20:45 BST on Tuesday 9 June in St Stephen's subway.
Two people saw the man, 29, in the early hours of Wednesday before he was found dead at 07:00 BST, police said.
A post-mortem examination revealed he died from injuries to the spleen and the death was declared "suspicious".
Det Insp Marie James said: "We are still trying to create a timeline of the man's final movements and the circumstances which led to his death.
"We would particularly like to hear from two people who saw the man in the early hours of Wednesday morning.
"Other witnesses have suggested a male teenager, possibly a college student, passed him in the subway at around 05:00 BST and later returned to buy flowers from the flower stall by the subway to leave inside.
"The second person we wish to trace is a man who gave assistance at the scene when his body was discovered.
"This man is described as being smartly dressed, wearing a jacket and glasses.
"I would also appeal again for people to contact me if they know details about any of his friends or family as we have still been unable to trace next of kin despite numerous inquiries."

Manchester United trainee Rothwell, 21, has penned a two-year deal.
The attacking midfielder made seven appearances in all competitions during a loan spell with Barnsley last season.
Maguire, 27, has signed a one-year deal after playing 25 games last season during a loan spell and subsequent short-term move from Rotherham.
Find all the latest football transfers on our dedicated page.
Russia has said bomb attacks which killed at least 140 people in Syria were aimed at "subverting attempts" to reach a political settlement.
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Police investigating the death of a homeless man in a Norwich subway want to speak to two potential witnesses.
[NEXT_CONCEPT]
Oxford United have signed midfielder Joe Rothwell on a free transfer and agreed a new contract with striker Chris Maguire.