Anthony Shadid reports: The Syrian government has launched a bloody assault to retake Homs, the country’s third-largest city, facing armed defectors who have prevented the government’s forces from seizing it as they did other restive locales this summer, in what may stand as one of the most violent episodes in an eight-month uprising.

The specter of civil war has long hung over Homs, the most tenacious and determined of cities opposed to President Bashar al-Assad’s rule, where the city’s Sunni Muslim majority has closed ranks behind the revolt. This month, parts of the city have become an urban battlefield, with activists saying government forces have killed 111 people in just five days, opposition groups warning of dire shortages forced by the siege and residents complaining of lawlessness by marauding soldiers and paramilitary fighters.

The strife comes as mediation by the Arab League has apparently collapsed in one of the latest efforts to end what is among the most ferocious crackdowns on the revolts sweeping the Arab world this year. The government has increasingly demonstrated it will continue to try to stanch dissent by force, ignoring the relatively muted protests of the international community.

As important, in a country fraught with fears of a broader civil war, Homs may be emerging as an example to the rest of Syria of the relative success of fighting back against a military that, while still unified, has suffered more defections as fighting persists and more than 3,000 civilians have been killed.

“Homs is a turning point for now,” said an analyst based in Damascus who spoke on the condition of anonymity. “It’s a successful model of self-defense, if you will, at a time when you really can’t expect people to take any more. They’ve seen too many corpses come back, too many people arrested, disappeared or returned after abominable treatment. It’s too much. And everybody seems to be losing control of the street.”