Activist groups in Hama said at least 200 civilians were killed by government artillery and snipers since the fighting in Hama started Sunday, The New York Times reported.
One activist said by telephone Saturday 200 tanks entered Hama before dawn, with security forces blocking residents from entering the city's mosques.
"The government has given up its responsibilities and handed everything over to the security forces," said Louay Hussein, a prominent opposition figure in Damascus. "They have lost their mind. They are acting without any strategic or political goal. The government's armed gangs are roaming the streets, simply looking for vengeance."
Fighting in Hama and other Syrian cities has brought condemnation from leaders in the United States, France and Germany, who accused Assad of using "indiscriminate violence" against protesters.
U.S. President Barack Obama called France's Nicolas Sarkozy and Germany's Angela Merkel to discuss new measures against Damascus, the White House said.
"The leaders condemned the Assad regime's continued use of indiscriminate violence against the Syrian people," the White House statement said.
"They welcomed the August 3 presidential statement by the U.N. Security Council condemning Syria's actions, but also agreed to consider additional steps to pressure the Assad regime and support the Syrian people," the statement said.
The White House statement didn't say what new measures it is considering.