The bombing last month that killed four top Syrian government figures and was followed by rebel offensives in Damascus and Aleppo that many hailed as a turning point in the battle to topple the government now looks more like a harbinger of worsening violence, not the beginning of the end.

Forces loyal to Syrian President Bashar Assad in the past week have launched a massive assault on rebel-held areas around the capital of Damascus and are seizing towns that had been thought to be secure rebel bastions. Loyalist forces are then conducting waves of raids, arrests and executions, according to anti-government activists.

The ferocity and seeming success of the government offensive undercut speculation that Assad’s government was crumbling after the July 18 bombing that killed four key military advisers and precipitated rebel actions in Damascus and Aleppo, the country’s largest city.

After initial gains in those cities, rebels forces now face the same dynamic that has reigned in other cities where fighting has gone on for much longer: The army lays siege to rebel-held areas, shells and bombs, and then launches raids that force the rebels to withdraw. When the offensive is over, the rebels filter back in.

Rebel spokesmen continue to offer upbeat assessments of their prospects. “The Free Syrian Army took control of six neighborhoods yesterday,” said Abdel Majeed Barakat, a member of Liwa Tawhid, a group fighting in Aleppo that has thousands of fighters under its command. The Free Syrian Army is the umbrella moniker adopted by the majority of the rebels.

But despite Barakat’s claims, most of Aleppo remains in government hands, the rebels have lost their major position in the Salahadin neighborhood, and fighting in the city has slowed in the face of fierce government attacks from the air that the rebels seem unlikely to withstand indefinitely, since they do not have anti-aircraft weapons.

Meanwhile, activists are reporting an increase of violence in Damascus, especially incidents of summary executions of fighters, activists and civilians.

“They think that will make civilians reject the Free Syrian Army,” said Abu Hassan, an anti-government activist in Damascus. “The security forces who carry these out wear masks.”

More than 200 civilians and rebels have been reported killed in Damascus on Wednesday and Thursday, and nearly 400 across the country. The Syrian government stopped releasing information about army casualties in June.

Darayya, a suburb south of Damascus where rebels claimed gains a month ago, has been under siege for a week, shelled heavily by artillery and subject to attacks by government helicopters and airplanes. Al Tal, another Damascus suburb that rebels appeared to take over last month, is reported by activists to be once more under the control of government forces. The same fate befell Jdedat Artouz, another suburb, where activists say dozens of summary executions took place.

Meanwhile, the government siege of areas that have long been battlegrounds continues unabated. An activist outside Homs, the country’s third largest city, said that government forces have enforced a blockade that has prevented supplies and people from entering rebel-held parts of the city, which the government continues to pound with artillery.

“There’s no food, not even cigarettes,” said the activist, who is based in a small city outside Homs that has become a hub for refugees and a staging ground for sending supplies inside.

“The humanitarian situation is dire and there is an urgent need for help. Diseases are spreading in areas where the dead cannot be collected, water is dirty and that is all that can be used as clean water is cut. Little food and electricity and medicines too,” reads one report on an activist message board.

In the country’s south, the government continues to press rebel forces as well. Earlier this week, government forces took al Harak, a suburb of Deraa, a city near the border with Jordan where the uprising against Assad began 18 months ago. On Wednesday, the rebels said they had reclaimed it, but on Friday it was still under government siege. Activists said 85 people had been killed there in the last six days.

Government forces also appear to have largely shut down rebel smuggling routes from Lebanon.

Communications in the country have becoming increasingly difficult, as the government has cut cellphone services in some areas for months and effectively jammed satellite equipment in many places.

Six months ago, many in the opposition’s ranks voiced the belief that if Assad began to use his air force, the West might intervene. But now that the Syrian helicopters and air power are being used regularly in Aleppo, Damascus and other parts of the country, the opposition has largely given up hope of international intervention.

“No one wants to be involved,” said Abu Hassan, the activist in Damascus.

Perhaps hoping to stir more Western outrage, activists are now accusing the government of using what they call “chemical weapons,” referring to munitions that include white phosphorus, a chemical that is frequently used to create smoke and that burns anything that it touches. Video posted on YouTube from the city of Rastan on Friday claimed to show the victim of one such attack, a young boy, on Thursday. Rastan is a now largely empty city of about 60,000 just north of Homs, on the main highway between Damascus and Aleppo. It, too, has been a battleground for months, with portions of the city entirely destroyed.

But the claims of white phosphorus use may not bring the kind of anger activists would like. Munitions containing white phosphorus are common and were used by U.S. forces in Fallujah, Iraq, in 2004, and by Israeli forces in the Gaza Strip in 2008 and 2009.