Secretary of State Hillary Clinton is calling on Syrian President Bashir Assad to "stop the slaughter" of peaceful protestors.
On Monday, government forces shelled the city of Hama and fired at worshippers heading to Ramadan prayers.
Syrian troops have continued to besiege the city as nearly 100 people across the country have been killed since Sunday. Hama has a history of defiance to the Assad family's 40-year dynasty in Syria.
The most recent military operations appears aimed at preventing protests from swelling during Ramadan, when Muslims throng mosques for special nightly prayers after breaking their fast. The gatherings could turn into large protests.
But the opposition remains defiant. Protests erupted Monday evening across the country, with hundreds turning out in cities including Homs, Latakia, the Damascus suburbs, and the eastern city of Deir el-Zour
The crackdown has sparked an international outcry and new European sanctions against members of Assad's regime. On Tuesday, Italy recalled its ambassador to Damascus, citing "horrible repression" of citizens.
President Obama called the attacks "horrifying." Secretary Clinton has also called for action from the U.N. Security Council.
Syrian forces have killed some 1,700 protestors since the uprising against the regime began earlier this year.