Rebel forces said Sunday that they had begun a co-ordinated offensive to “liberate” Aleppo, the largest city in Syria, while government troops backed by helicopters fought back in Damascus to regain control of rebel-held neighbourhoods.

The attack on Aleppo, Syria’s commercial centre that has been a bastion of support for President Bashar Assad, was a sign of a growing confidence among rebel troops. The surge in confidence comes days after a bombing killed four members of Assad’s inner circle in Damascus.

Brig. Gen. Abdul Kareem al-Ahmad of the rebel Free Syrian Army said during a meeting in Turkey that Assad and his circle are showing signs of weakness.

"Right now, Assad's inner circle has been dismantled and Assad has lost his balance," said al-Ahmad. "This war is now being waged in the heart of Syria in Damascus."

The recent killings of senior regime officials, a series of high-level military defections and the capture of important border crossings have given the rebels momentum over the past week and have put the regime back on the defensive.

After fighting for nearly a week to quell the rebel attacks inside the capital, regime forces appeared close to winning back control of Damascus.

Assad’s days numbered?

Many analysts believe that now that the fighting has reached Syria’s cities, the regime’s days are numbered.

Bessma Momani, a senior fellow at the Centre for International Governance Innovation in Waterloo, Ont., told CTV News Channel that the fighting in Damascus and Aleppo signals at least the beginning of the end for Assad’s regime.

“We are in the final chapter,” she said of Assad’s rule. “Once the rebels are able to hold and control Damascus, particularly after what I anticipate are continued defections, I think we will see the end of this regime.”

Momani said preparations should begin immediately for the post-Assad period.

“That’s an imperative conversation that we haven’t even started into-- which is ‘What happens on the day after?’” she said.

“It’s incumbent on the international community to really focus a lot of diplomatic efforts on that front.”

Failure to begin planning for the post-Assad period can lead to a “lawlessness and chaos,” on a level similar to what was witnessed in Iraq and the former Yugoslavia,” she said.

Momani said the international community should immediately begin drafting reforms for the Syrian security sector, political organizations and constitution.

She also criticized Friday’s extension of the UN observer mission, saying the 300-member observer team has largely been “holed up in a hotel” in Damascus for weeks due to the escalating violence.

Now that the rebels are in Damascus, the violence will only increase further diminishing power of the observers, she said.

Threats of a regional crisis

The battles in the two heavily populated cities signify the beginning of a new and bloody stage in Syria’s civil war.

With the conflict moving from the countryside into Syria’s urban centres, activist groups say the death toll has risen to more than 19,000 since the conflict began in March 2011.

The Syrian Observatory for Human Rights also said July will soon become the deadliest month of the uprising so far, with nearly 2,752 people killed in the first three weeks.

The increasing bloodshed is threatening to flood across borders and develop into a larger regional conflict. Neighbouring countries, particularly Israel, are carefully watching the events in Syria unfold.

Israeli Prime Minister Benjamin Netanyahu said in an interview with Fox TV that his chief concern is the chaos that might ensue if Assad falls and the Syrian- and Iranian-backed group Hezbollah acquires access to the Syrian supply of chemical weapons, rockets and missiles.

Netanyahu said Israel hasnot considered crossing the border into Syria and seizing the weapons.

"There are other possibilities," he said. "We'll have to consider our actions. ... Do I seek action? No. Do I preclude action? No."

There have been no signs that Shiite Hezbollah is currently active in Syria, where the rebel forces are largely Sunni.

Meanwhile King Abdullah of Saudi Arabia, a Sunni power and major regional rival of Iran, has announced plans to start a campaign to collect donations to “support our brothers in Syria.”

The announcement suggested the country may be looking to increase its funding for the rebels, which many believe they are already doing.

The fight for Syria’s border points

Recently the rebels have won control of several border points with Iraq and Turkey. An online video posted by activists Sunday showed groups of gunmen in front of the newly won Bab al-Salamah crossing on the Turkish border. The gunmen celebrated as they raised the Syrian opposition flag over the crossing. It was the second Turkish border point captured in a week.

Yet for every crossing won, others have been abandoned or lost. Iraqi military officials and state television reported that the Syrian government forces won control of the northern Rabiya border crossing after the rebels withdrew.

Still, Brig. Gen. Manaa Rahal of the Free Syrian Army celebrated the seizures of the Turkish border crossings.

"The seizure of these border crossings was a crucial victory for the opposition and its strategic importance will only increase," he said in a meeting in Turkey's Hatay province.

Damascusand Aleppo, are the country's largest cities with populations of 2.5 million and 3 million, respectively. 

Both cities are home to elites with close ties to the president’s government, as well as commercial classes and minority groups who worry their status will diminish if Assad falls.

Col. Abdul-Jabbar Mohammed Aqidi, the commander of a new confederation of rebel groups named the Unity Brigade, called on government troops to abandon Assad and join the opposition.

He said rebels will protect those belonging to Assad's Alawite minority sect, a small sect of Shiite Islam. “Our war is not with you but with the Assad family," he promised.

Controlling the message

Meanwhile the battle for Aleppo rages on.

The Britain-based Syrian Observatory for Human Rights and Aleppo-based activist Mohammed Saeed said the fighting is heavily concentrated in several areas of the city.  

"Aleppo is witnessing serious street battles," said Saeed.

Fierce fighting is raging on the road leading to the city's international airport, as rebels try to prevent the regime from sending more troops.

However, Syrian state TV downplayed the violence, saying government troops were successfully hunting down “terrorists” and killing them.

Heavy fighting was also reported in Damascus in the neighbourhoods of Mazzeh and Barzeh that once belonged to the rebels. Local papers reported heavy casualties as government troops used helicopters during the attacks.

State TV denied claims that government troops were using helicopters in the capital, saying the capital was calm and troops were simply closing in on terrorists. Images were shown of quiet streets in Damascus, in an effort to portray a capital that had returned to normalcy.

With files from The Associated Press