WASHINGTON >> President Barack Obama is stepping up his criticism of Syria’s crackdown on protesters, charging that the Syrian president is "completely incapable and unwilling" to respond to what Obama calls the legitimate grievances of the Syrian people.

Dozens of people were reported killed Sunday as Syrian security forces escalated their response to protests against President Bashar Assad. In the city of Hama, a barrage of shelling and gunfire left bodies scattered in the streets.

Obama issued a statement Sunday saying he is "appalled" by the violence and brutality the Syrian government has aimed at its own people. He calls the reports from Hama "horrifying" and says they demonstrate the true character of the Syrian regime.

Obama says the U.S. will continue to increase pressure on the Syrian regime. 

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.

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 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.

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."

But months of withering criticism and sanctions by the international community has not softened the regime’s crackdown. Assad has brushed off the criticism as foreign interference.

More than 1,600 civilians have been killed in the crackdown on the largely peaceful protests against Assad’s regime since the uprising began. Most were killed in shootings by security forces at anti-government rallies.

The government has sought to discredit those behind the protests by saying they are terrorists and foreign-backed extremists, not true reform-seekers. State-run news agency SANA blamed the unrest Sunday on gunmen and extremists, and said two policemen, an officer and two soldiers were killed.

Since the uprising began, Hama has been one of the hottest centers of the demonstrations, with hundreds of thousands protesting every week. In early June, security forces shot dead 65 people there before pulling out. Until Sunday, the troops have stayed on the outskirts, ringing the city and conducting overnight raids.

In 1982, Assad’s father, Hafez Assad, ordered the military to quell a rebellion by Syrian members of the conservative Muslim Brotherhood movement. The city was sealed off and bombs dropped from above smashed swaths of the city and killed between 10,000 and 25,000 people, rights groups say.

The real number may never be known. Then, as now, reporters were not allowed to reach the area.

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Associated Press writers Dale Gavlak in Amman, Jordan, and David Stringer in London contributed to this report.