Forces of Syria's President Bashar al-Assad walk near the glass factory in Jubaila village in the countryside of north-east Aleppo after regaining control of the area. (George Ourfalian/Reuters)

Syrian government forces have dramatically intensified air and ground assaults on areas held by moderate rebels, attempting to deliver crippling blows as world attention shifts to airstrikes by a U.S.-led coalition against Islamic State militants in Iraq and Syria.

Since Monday, Syrian aircraft have targeted Aleppo in the north, the eastern suburbs of Damascus and southern areas near the Jordanian border, launching more than 210 airstrikes, said Rami Abdulrahman of the Britain-based Syrian Observatory for Human Rights, a group that monitors the civil war.

Rebels in Aleppo say President Bashar al-Assad’s military has escalated attacks in northern areas of the city, trying to cut the supply lines of opposition fighters inside Aleppo.

“During the last three days, we have been hit by over 120 barrel bombs,” said Ahmed Abu Talal, a rebel belonging to the Islamic Front group, referring to particularly deadly high-explosive bombs that are often dropped by helicopter.

Syria’s military has virtually encircled the city with the help of Shiite militias from Lebanon and Iran, the Assad regime’s chief ally. Iranian and Iraqi news sites reported that a general from Iran’s Basij militia, identified as Drisawi Jabbar, was killed fighting near Aleppo last week.

Men walk on the rubble of damaged buildings at a site hit by what activists said were airstrikes by forces of Syria's President Bashar al-Assad in Damascus on Monday. (Bassam Khabieh/Reuters)

Abu Talal said pro-government forces are trying to take the village of Handarat, which is located just north of Aleppo and next to one of the last roads connecting the city’s rebels with reinforcements and food brought in from the Turkish border.

The fall of that road would constitute a major blow to Assad’s opposition in a three-year-old civil war that has killed nearly 200,000 people.

“They are very close to the area now,” said Abu Talal, speaking via Skype from northern Aleppo.

Rebels and analysts say Assad’s forces are increasing their attacks to exploit what the regime sees as a window of opportunity opened by a campaign that Washington and its allies launched last month against the Islamic State, a heavily armed al-Qaeda offshoot that is also known as ISIS or ISIL.

The U.S.-led coalition, which includes Arab states such as Saudi Arabia and the United Arab Emirates, has carried out hundreds of airstrikes against the radical Islamist group, which has captured swaths of territory from Iraq to north-central Syria.

“The Assad regime senses opportunity at the moment because the world’s attention is shifting to ISIS,” said Emile Hokayem, Middle East analyst at the London-based International Institute for Strategic Studies.

The regime has stepped up aerial bombardment of the rebel-held suburbs of eastern Damascus, as well as in areas near the city of Idlib. Government helicopters have dropped some 45 barrel bombs in recent days in the countryside near Idlib to halt rebel movements near two military bases on a strategic road connecting Aleppo with Hama, to the south, said Abdullah Jabaan, a resident of Idlib and journalist for the Syria Live News Network, which supports the opposition.

He said 55 people were killed and more than 100 others wounded in those attacks.

Meanwhile, Assad’s military has largely avoided territory held by Islamic State militants, instead striking moderate rebel factions that could be slated to receive weapons and military training from the coalition, said Riad Kahwaji, chief executive of the Dubai-based Institute for Near East and Gulf Military Analysis.

“If the regime manages to fully besiege Aleppo at this time, they would block and undermine the plans of the alliance to use the opposition, or at least present the opposition, as the ultimate ground force to deal with ISIS,” he said.

A successful routing of those rebels could position the Assad regime as the only force in Syria capable of fighting the Islamic State, he said.

Syrian officials have welcomed the coalition strikes on Islamic State fighters in the country, but the United States says it rejects any coordination with the Assad government.

Many of those airstrikes have targeted Islamic State militants mounting an assault on the Kurdish town of Kobane, nestled along Syria’s northern border with Turkey. Starting over a month ago, the coalition attacks have helped Kurdish fighters fend off the onslaught, although the jihadists persist.