Syrian tanks have stormed the city of Hama killing at least 45 civilians, a leading rights group says.
Earlier, a doctor confirmed that 24 people had been killed and residents reported "intense gunfire" as Syrian forces moved in from several sides.
The doctor also said there are scores of wounded people and a shortage of blood for transfusions.
Speaking in London, Rami Abdel Rahman of the Syrian Observatory for Human Rights said the latest toll, based on his contacts with Syrian activists, was 45 dead and several more wounded.
Hama, a hub of anti-government protest, has been besieged for nearly a month.
Opposition activists in Syria are also reporting army raids on the cities of Deir el Zoor in the east and Deraa in the south.
There are unconfirmed reports of security forces arresting dozens of residents in both cities.
In the capital Damascus, there are reports one suburb has been sealed off by the army.
The army is signalling that it will not tolerate large scale unrest ahead of the month of Ramadan, when protests are expected to grow reports the BBC.
Hama is Syria's fourth largest city and has a population of about 700,000.
Syria has seen more than four months of protests against the rule of the President, Bashar al-Assad.