Syrian forces killed nearly 140 people on Sunday including at least 100 when the army stormed the flashpoint protest city of Hama, activists said, prompting calls for emergency Security Council talks.
Activists said it was one of the deadliest days in Syria since demonstrators first took to the streets on March 15 demanding democratic reforms before turning their wrath on the regime and calling for its ouster.
As reports of the brutal pre-Ramadan crackdown on Hama unfurled, US President Barack Obama and European leaders condemned the crackdown as Germany and Italy called for an urgent meeting of the UN Security Council.
A meeting could be held on Monday. But the move is likely to reopen bitter divisions within the Security Council, which has not yet been able to agree even a statement on President Bashar al-Assad's crackdown against opponents.
"It is one of the deadliest days" since the protests erupted, said Rami Abdel Rahman, the head of the Britain-based Syrian Observatory for Human Rights.
Rights activists said at least 136 people were killed across Syria and expected the toll to rise, while scores were wounded.
"One hundred civilians were killed on Sunday in Hama by gunfire from security forces who accompanied the army as it stormed the city," said Abdel Karim Rihawi, head of the Syrian League for the Defence of Human Rights.
Rihawi said five other people were killed in the central city of Homs and three more in the northwestern province of Idlib when security forces opened fire on protesters who rallied in support of Hama.
The head of the National Organisation for Human Rights, Ammar Qorabi, put the Hama death toll at 95. The Observatory's Abdel Rahman said at least 47 people were killed in and around the central city.
"The number of those wounded is huge and hospitals cannot cope, particularly because we lack the adequate equipment," he added, quoting a Hama hospital source.
Abdel Rahman said the Hama crackdown came after more than 500,000 people rallied in the city on Friday after Muslim prayers during which a cleric told worshippers "the regime must go".
Activists also reported deaths in Deir Ezzor, Syria's main gas- and oil-production hub in the east, which has become a rallying point for protests along with Hama.
At least 19 people were killed in Deir Ezzor, six in Herak in the south, and one in Al-Bukamal in the east, said Qorabi, adding most of those shot in Deir Ezzor were "hit in the head and the neck" by snipers.
Abdel Rahman meanwhile told AFP that protesters set ablaze 24 army troop carriers in the Masrib region west of Deir Ezzor. "They threw Molotov cocktails on a military convoy to stop it from advancing on Deir Ezzor and set ablaze 24 troop carriers."