Updated at 6:14 p.m. ET
BEIRUT - Syrian security forces backed by tanks and snipers launched a ferocious assault Sunday on defiant cities and towns, killing at least 80 people and possibly many more as the regime raced to crush dissent ahead of Ramadan. Corpses littered the streets after a surge in violence that drew widespread international condemnation.
Estimates of the death toll, which were impossible to verify, ranged from around 75 people to nearly 140 on a day when the attacks began before dawn and witnesses said they were too frightened to collect corpses from the streets.
The worst carnage was in Hama, the scene of a 1982 massacre by President Bashar Assad's late father and predecessor and a city with a history of defiance against 40 years of Assad family rule. Hospitals there were overwhelmed with bloodied casualties, suggesting the death toll could rise sharply, witnesses said.
President Obama called the reports "horrifying" and said Assad is "completely incapable and unwilling" to respond to the legitimate grievances of the Syrian people.
Ramadan, which begins Monday, will present a critical test for the government, which has unleashed deadly firepower since March but still has not been able to put down the revolt. Daily demonstrations are expected to surge during the holy month, when crowds gather in mosques each evening after the dawn-to-dusk fast.
Though the violence has so far failed to blunt the protests, the Syrian government appears to be hoping it can frighten people from taking to the streets during Ramadan. The protesters are promising to persevere.
Having sealed off the main roads into Hama almost a month ago, army troops in tanks pushed into the city from four sides before daybreak. Residents shouted "God is great!" and threw firebombs, stones and sticks at the tanks, residents said.
By mid-morning, the city looked like a war zone, residents said. The crackle of gunfire and thud of tank shells echoed across the city, and clouds of black smoke drifted over rooftops.
"It looks like Beirut," said Hama resident Saleh Abu Yaman, likening his hometown to the Lebanese capital that still bears the scars of nearly two decades of civil war.
Syria has banned most foreign media and restricted coverage, making it difficult to confirm events on the ground. But interviews with witnesses, protesters and activists painted a grim picture Sunday of indiscriminate shelling and sniper fire as residents fought back by erecting barricades and throwing firebombs at their assailants.
It appeared the regime was making an example of Hama, a religiously conservative city about 130 miles (210 kilometers) north of the capital, Damascus. The city has largely has fallen out of government control since June as residents turned on the regime and blockaded the streets against encroaching tanks.
The United States and France enraged the government earlier this month when their ambassadors traveled to Hama in a trip designed to demonstrate solidarity with demonstrators.
But Sunday's deadly siege only ignited more calls for defiance among protesters.
The Local Coordination Committees, which helps organize anti-government protests, urged people to take to the streets and start a general strike to protest the killings.
"If you don't unchain yourselves now and save your country now, you will be ruled like slaves for years and decades to come," the group said.
An escalation in violence during Ramadan, a time of heightened religious fervor for devout Muslims, would bring a new dimension to the unrest in Syria, which has reached a stalemate in recent weeks. Assad's elite forces have waged nearly nonstop crackdowns around the country, but new protest hotbeds have emerged taxing the already exhausted and overextended military.
There have been credible reports of army defections, although it is difficult to gauge how widespread they are. Assad, and his father who ruled before him, stacked key military posts with members of their minority Alawite sect, melding the fate of the army and the regime.
The army has a clear interest in protecting the regime because they fear revenge attacks and persecution should the country's Sunni majority gain the upper hand.
The searing August heat will only compound the already combustible scenario.
In London, British Foreign Secretary William Hague said the attacks were "all the more shocking" on the eve of Ramadan and appeared to be part of a coordinated effort to deter Syrians from protesting during the holy month.
"President Bashar (Assad) is mistaken if he believes that oppression and military force will end the crisis in his country. He should stop this assault on his own people now," Hague said.
Italian Foreign Minister Franco Frattini appealed to the Syrian government "to immediately cease the violence against civilians," calling it "a horrible act of violent repression against protesters who have been demonstrating for days in a peaceful manner."
U.N. Secretary-General Ban Ki-moon called for an end to the violence and reminded Syrian authorities that "they are accountable under international human rights law for all acts of violence perpetrated by them against the civilian population."