People carry a body of a person killed in clashes between rebels and Syrian government forces in Aleppo, Syria, on July 27, 2012. (Alberto Prieto/AP)

Syrian forces launched a fresh assault Friday in the country’s largest city, Aleppo, while residents prepared for a broader offensive in the latest government stronghold to be transformed into a battleground.

As Western powers warned of an impending massacre and the former chief of the U.N. peacekeeping mission in Syria said it was a “matter of time” before President Bashar al-Assad’s government fell, heavy automatic-weapons fire was unleashed in what activists said was a lethal attack on Aleppo’s rebellious Firdous district.

The latest security force operation came amid reports of troops and tanks massing outside the once tightly controlled city, whose path to conflict corresponds to the growing horror many Syrians have voiced in the face of accounts of persistent government brutality.

“You heard the planes spreading some love on the people?” one man in Aleppo’s old city asked acidly, after several long bursts of what sounded like helicopter gunfire.

Firdous is one of a number of districts where fierce clashes have occurred since the rebel Free Syrian Army took its fight to the capital, Damascus, and Aleppo, the country’s commercial hub, last week. The human rights advocacy group Avaaz put the death toll in Firdous at 17, including five children, in what it described as a sustained assault with tanks, mortars and helicopter gunships.

The British government echoed the United States in condemning the Assad government’s “vicious assault” on civilians in the city, who it said were “threatened with a potential massacre.”

Norwegian Maj. Gen. Robert Mood, who last week ended his tenure as head of the U.N. peacekeeping mission to monitor Syria’s cease-fire, told Reuters news service it was “only a matter of time” before the fall of the regime that he said was using “such heavy military power and disproportional violence against the civilian population.”

The battle in Aleppo comes amid anecdotal but tangible signs of a shift in sentiment among members of the civilian population there.

As in other big cities, brutal crackdowns in residential areas where rebels are active appears to make the government more and more enemies among those who are affected — or who simply hear of what is happening.

Hundreds of people gathered in Aleppo’s Ashrafiya district Thursday night for a demonstration in which they set off fireworks and called for the overthrow of Assad and justice for Syrians. Families watched and street life went on as normal in the vicinity, a scene local activists said would have been unthinkable last year, when the numbers of protesters were tiny, the crowds around them often hostile and the security forces never far away.

“When we began, we were only 15 people, and everyone was against us because they said we were bringing war here,” said an activist known as Doljan. “But now it has changed after they saw the shelling. Now they believe they can say what they want.”

Like other cities, Aleppo has seen an influx of refugees — some now from within its own boundaries — bearing stories of government-backed violence. One resident who fled shelling in the city of Homs earlier this year said some Aleppo residents had at first accused her of being a terrorist but later began to change their views.

“When I told them that I left with only the clothes on my body, some said: ‘We are already preparing our bags because we know it will be our turn next,’ ” she said.

While prominent members of Aleppo’s influential business community apparently remain loyal to Assad — and say they are being violently targeted by the opposition for doing so — some have quietly been funding opposition groups or relief work.

Grass-roots supporters of Assad remain in Aleppo, some arguing that the government is the only guarantor of stability against an opposition made up of foreign-backed terrorists.

Many Assad loyalists also cite abuses that some armed rebels are carrying out — and that many opposition activists acknowledge and deplore.

One Aleppo resident told of being forced to pay a ransom of $6,200 after his van was hijacked outside the city by gunmen he suspected were opposition fighters.

“Those criminals are destroying the country,” another resident said, noting the conflict-driven insecurity, economic damage and long-running shortages of fuel and other goods in a city whose supply routes have been choked by battles in the surrounding countryside.

Few appear to expect Aleppo to fall quickly to a rebel army that has only the most tenuous control over the areas it occupies, enforced by an arsenal that is puny compared with the government’s Russian-supplied arms. But each booming security force assault in the city is also a shot fired in the battle for hearts and minds, chipping away at the government’s claim that it is the protector of all the country’s people.

One man in the rebel-controlled Salaheddin district said he was unhappy that the Free Syrian Army had proclaimed their takeover of the area, as he knew instinctively what the government’s response would be.

“We know those in this regime are killers,” he said. “They would even shell their own mothers.”