Human Rights Watch urged the United Nations Thursday to impose an arms embargo on the Syrian government after air strikes on a rebel town near the capital killed more than 100 people.
The New York-based group said the Sunday attack on Douma showed the government's "appalling disregard for civilians".
The series of strikes, several of which hit a crowded marketplace in the Eastern Ghouta region town, killed mostly civilians.
"This latest carnage is another reminder -- if any was still needed -- of the urgent need for the (UN) Security Council to act on its previous resolutions and take steps to stop indiscriminate attacks," HRW deputy Middle East director Nadim Houry said.
The Syrian Observatory for Human Rights, a Britain-based monitor, said Thursday that 117 people had been killed.
That was up from a previously reported figure of 96 because of people who died from injuries sustained in the strikes.
Foreign Minister Walid Muallem defended the attacks in comments to an Egyptian television station published Thursday by Syria's official news agency SANA.
"It is natural for the Syrian government to use the appropriate tools to defeat terrorism," he said.
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"But many of the terrorists use civilians as human shields, so what is claimed about massacres in Douma or elsewhere is fabricated news."
The incident was among the deadliest government assaults in the conflict, which began in March 2011.
It came almost two years after a chemical weapons attack on Eastern Ghouta that the United States said killed 1,400 people.
Much of the international community blamed Syria's government for that attack, though it denied responsibility.
HRW noted that Douma, as well as other parts of the rebel bastion of Eastern Ghouta, are regularly targeted in regime air strikes that disproportionately kill civilians.
The group also criticised rebels operating in the area for firing indiscriminately at civilians in nearby government-held territory, including Damascus.
HRW said the Security Council was failing to enforce its own resolutions calling for an end to attacks on civilians and the indiscriminate use of weapons in crowded places.
It urged the UN to monitor such attacks, attribute responsibility for them and sanction those to blame.
"How many more lives will be lost before the Security Council enforces its own words?" Houry asked.