But those provinces Raqqa, Hassakeh and Deir el-Zoura are located hundreds of miles (kilometers) from the capital. Rebel advances there pose no direct threat to the regime's hold on Damascus the ultimate prize in the civil war and any effort to claw back the lost territory would demand manpower and military hardware, neither of which the regime is inclined to invest at the moment.
Instead, it has used its remaining airbases and military outposts in those areas to shell and bomb the territory it has lost in an attempt to forestall the opposition from establishing an interim administration in the rebel-held regions.
"What's important for the regime is not to leave any buffer zone, or any security zone for the rebels," said Hisham Jaber, a retired Lebanese army general who heads the Middle East Center for Studies and Political Research in Beirut.
While keeping the rebels off-balance in the lands it has lost, the regime at the same time has dedicated its resources to Damascus and securing what it widely believed to be Assad's Plan B a retreat to the Mediterranean coastal region that is the heartland of his Alawite minority, which views its own survival as being tightly intertwined with that of the regime.
Key to that strategy is control of the corridor running from Damascus to the city of Homs and from there to the coast.
Fighting has flared in the Homs region in recent weeks as the government has pressed its campaign to stamp out rebel-held pockets in the area.
Much of the heaviest fighting has raged near the Lebanese border around the town of Qusair, southeast of Homs, where activists said government troops backed by gunmen linked to Lebanon's Lebanese Shiite militant Hezbollah group captured the villages of Radwineyeh and Tel al-Nabi Mando.
"The Qusair area is highly important," said Elias Hanna, a retired Lebanese general and a senior lecturer at the American University of Beirut. "It is critical for Assad because this area is the backyard of Damascus. It is the link between Damascus, Homs and the coastal area, so he can ill afford to lose it."
As government troops have pursued rebels in the Qusair region, regime forces in and around Damascus have also moved against opposition-held suburbs, which anti-Assad fighters have tried to use as a springboard for forays into the capital itself.
With the stakes so high in the battle for the capital, the fighting around Damascus has been particularly fierce, and the regime has used its warplanes and artillery to try to pound rebellious areas into submission.
On Sunday, regime troops seized the suburbs of Jdaidet Artouz and Jdaidet al-Fadel after days of fighting.
Activists said Monday that more than 100 people and possibly many more were killed in the two neighborhoods, about 15 kilometers (10 miles) southwest of Damascus.
The Britain-based Syrian Observatory for Human Rights said it has documented 101 names of those killed, including three children, 10 women and 88 men. It added that the death toll could be as high as 250.
The Local Coordination Committees, another activist group, put the death toll at 483. It said most of the victims were killed in Jdaidet Artouz.
The Observatory and the LCC both rely on a network of activists on the ground in different parts of Syria.
Syria's state news agency said Syrian troops "inflicted heavy losses" on the rebels in the suburbs.
A government official in Damascus told The Associated Press that rebels were behind the killings in Jdaidet al-Fadel. The army found decomposed corpses there after entering the area, said the official, who spoke on condition of anonymity because he was not authorized to talk to the media.
Jdaidet al-Fadel is inhabited mostly by Syrians who fled the Golan Heights after the area was captured by Israel in 1967. Jdaidet Artouz has a large Christian and Druse population two minority communities that have generally stood by Assad or on the sidelines.
The killings appeared reminiscent of violence in the Damascus suburb of Daraya in August. At the time, activists said days of shelling and a killing spree by government troops left 300-600 dead.
Mohammed Saeed, an activist based near Damascus, said the rebels withdrew as soon as the government offensive began last week. After that, he said via Skype, troops and pro-government gunmen stormed the area and over several days killed about 250 people.
"The situation is very tense," Saeed said, noting that the area has no electricity, water, or mobile phone service. "There is widespread destruction in Jdaidet al-Fadel, including its only bakery."
Death tolls in the civil war often conflict, especially in areas that are difficult to access because of the fighting. The government also bars many foreign journalists from Syria.
The main opposition group, the Cairo-based Syrian National Coalition, described the killings as "the latest heinous crime committed by the Assad regime." It said in a statement that "the deafening silence of the international community over these crimes against humanity is shameful."
The opposition has clamored for more support from its international allies, particularly in the form of heavier weapons that could level the playing field against Assad's superior firepower. The U.S. and its allies have so far balked at the idea, fearing that such arms could fall into the hands of extremists fighting in the rebel ranks and be used later against Western or Israeli targets.
But the opposition has received a recent boost in support.
On Monday, the European Union lifted its oil embargo on Syria to province more economic support to the rebels. The decision will allow for crude exports from rebel-held territory, the import of oil and gas production technology, and investments in the Syrian oil industry, the EU said in a statement.
The move marks the first relaxing of EU sanctions on Syria in two years as governments try to help ease shortages of vital supplies in areas held by the opposition.
The decision follows a pledge from the U.S. over the weekend to give an additional $123 million in non-lethal aid to the Syrian opposition. That could include for the first time armored vehicles, body armor, night-vision goggles and other defensive military supplies, officials said.
In northern Syria, gunmen kidnapped two Syrian bishops Monday who were traveling from the Turkish border to the city of Aleppo, a church official said.
It was not immediately clear who abducted Bishop Boulos Yazigi of the Greek Orthodox Church and John Ibrahim of the Assyrian Orthodox Church, said Greek Orthodox Bishop Tony Yazigi. Boulos Yazigi is the brother of John Yazigi, the Eastern Orthodox patriarch of Antioch.
They are the highest level clerics to be abducted in the civil war.
Associated Press writers Bassem Mroue in Beirut and Albert Aji in Damascus, Syria, contributed to this report.