Syrian troops on Monday routed government opponents in a neighborhood of Homs that had emerged in recent weeks as a center of armed resistance to the regime led by President Bashar al-Assad, dealing what appeared to be a serious setback to the protest movement and to an Arab League peace initiative designed to end the violence.

Homs residents and human rights groups said security forces stormed the Bab al-Amr neighborhood in the small hours of the morning, concluding a six-day assault in which dozens were killed and scores injured, many of them in tank bombardments.

Defected soldiers who had been defending the protest hot spot either fled to the surrounding countryside or were captured or killed, said residents and activists. Syrian troops combed through the neighborhood Monday detaining all the young men they encountered, and government supporters staged a noisy demonstration through the deserted streets.

The assault came as Assad’s government braced for the potential fallout from its failure to abide by the terms of an Arab League-sponsored peace initiative agreed to last Wednesday. Under the deal, Syria was to withdraw troops from cities, allow peaceful protests and release detainees.

Instead, the army launched an offensive in Homs, surrounding Bab al-Amr on the eve of the league’s announcement of the deal in Cairo and bombarding it with tank fire.

The offensive was accompanied by a surge in retaliatory sectarian killings in which hospital workers and human rights groups have said at least 70 people died, illustrating the potential for this religiously mixed city in the heart of Syria to serve as a crucible for a civil war many have feared since the uprising erupted in March.

For three days last week, members of the Sunni majority and the Alawite minority, to which Assad belongs, targeted one another in sectarian killings.

Those attacks appear to have abated in the past few days, but the military’s offensive has not. On Monday evening, several activists said a fresh government force of about 5,000 was seen assembling at the southern approaches of the city, apparently in preparation for an assault on other neighborhoods.

The Local Coordination Committee, which monitors and supports protests, said at least 40 civilians had been killed in the Homs offensive since the league peace plan was announced. Rami Abdelrahman of the London-based Syrian Observatory for Human Rights said the death toll could be higher because many injured civilians were unable to reach hospitals.

Abdelrahman said that at least 30 defected soldiers died in a final pitched battle to defend the neighborhood Sunday, before the survivors fled. A medical worker at one of the city’s hospitals saw tanks firing at each other, suggesting some of the defected soldiers had access to significant firepower.

Medical teams that ventured into streets on the outskirts of the neighborhood Monday found the bodies of seven civilians who apparently had been injured in the bombardments but were unable to reach hospitals, said the medical worker, who was reached via Skype and spoke on the condition of anonymity because he feared for his safety.

Opposition groups said the assault demonstrated that the Syrian government was not serious about the peace deal, and they again appealed to the international community to provide protection for civilians.

The Syrian National Council, the umbrella organization formed last month in Istanbul to represent the opposition, said that Homs should be declared a “disaster” zone and that the international community should act to provide medical relief and monitors.

Arab leaders have effectively declared the initiative dead, and Qatar has summoned an emergency meeting of the league to address next steps against Syria.

But the emergency meeting won’t take place until Saturday, and Syrian activists accused Arab leaders of slowing their response to give the government time to crush the revolt in this last major opposition stronghold. The Syrian Revolution General Commission, which represents several protest groups inside Syria, urged the league to meet sooner and “not to give the regime another opportunity to bombard, strike and burn.”

Homs has emerged in recent months as the epicenter of the nearly eight-month-old revolt, replacing the city of Hama after protests there that drew hundreds of thousands of people to a central square were crushed in August.

The sprawling, working-class Bab al-Amr neighborhood on the southeastern edge of the city, where dozens — and, some say, hundreds of defected soldiers — had gathered to defend protesters and keep government forces out, had become the focus of the opposition movement in the city.

The crushing of yet another protest hot spot suggests the government’s strategy of relying on overwhelming force to quell the uprising is working, at least for now. The uprising has emerged as the most serious challenge to four decades of Assad family rule.

But human rights activists pointed to the persistence of protests in other parts of the country that apparently had been crushed, including the southern town of Daraa and Hama, where demonstrations have been staged in recent days.

“It’s bad news in the short term but not in the long term,” Abdelrahman said. “The Syrian regime can win a battle, but we are sacrificing our blood and we will win the war.”