At least 56 people have reportedly been killed in further shelling of Syrian cities, amid widespread anger at China and Russia's move to block a UN resolution on the crisis.
The Syrian Observatory for Human Rights reported the figure, which follows claims of more than 300 deaths at the beginning of the weekend.
Half of those killed in the latest flashpoints were civilians in the cities of Homs, Daraya and Idlib, according to the UK-based group.
The news came as Arab and Western leaders pledged to continue attempts to end the violence in Syria.
British Foreign Secretary William Hague agreed Russia and China had "blood on their hands" and that their veto had emboldened President Bashar Assad's regime.
The vote came a day after Syrian security forces bombarded the city of Homs - and are thought to have killed around 350 people in the worst night of bloodshed of the 11-month uprising.
France has suggested the EU will strengthen sanctions against Syria in the wake of the veto.
And Mr Hague told Sky News' Murnaghan show that while military action was not being contemplated, a decision had not been made about whether diplomatic ties with Damascus would be cut.
He backed Arab League plans to press ahead with efforts to secure a peaceful political transition.
"This is a doomed regime as well as a murdering regime," he said.
"There is no way it can get its credibility back, internationally or with its own people. It's when you realise that you see what a mistake Russia is making by backing this regime to the very end.
"The main way forward now is for the Arab League to pursue their plan in any case," he said.
"They do not need the permission of the United Nations, although it would have been good to have a clear mandate.
"They should pursue their plan, they should intensify their own pressure on the Assad regime to stop the killing and allow a peaceful political transition.
"Arab League foreign ministers are meeting in a few days' time. We will be having discussions with some of them and will encourage them very much to intensify their own pressure."
Former Prime Minister Sir John Major told the BBC's Andrew Marr show that Russia and China were "effectively giving the green light for a pretty bad regime to murder people".
He added that the UN should spearhead moves to resolve the crisis through diplomatic means.
US Secretary of State Hillary Clinton joined international condemnation of the veto, saying: "What happened yesterday at the United Nations was a travesty."
Colonel Riad al Asaad, commander of the rebel Free Syrian Army, said the failure of the UN Security Council resolution meant "there is no other road" except military action by his fighters to topple President Assad.
He described the veto as a "strike against the Syrian people," not just the opposition.
But the Arab League's secretary-general Nabil Elaraby said in a statement that the veto "does not negate that there is clear international support for the resolutions of the Arab League".
Meanwhile, video purportedly shot on Sunday in Homs appeared to show evidence that residential areas were being shelled, although Sky News has no way of verifying the footage.
Other videos, which have appeared on social media websites and are also not possible to verify, featured graphic images of injuries apparently suffered by Homs residents including children.
The bloc's resolution had called for President Assad to step down so talks with the opposition could start.
Russian Foreign Minister Sergei Lavrov is due to visit Syria on Tuesday, when his ministry said he would push for speedy democratic reforms.
"Russia strongly intends to achieve a rapid stabilisation of the situation in Syria through the rapid implementation of much-needed democratic reforms," the ministry said in a statement.
It comes after protesters attacked the Syrian embassy in London, breaking down barricades and hurling missiles at the building.
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