Russian and Syrian jets on Saturday flew bombing raids on a suburb of Syria's second city of Aleppo after jihadi insurgents took control of most of the city in a surprise offensive, a war monitor and military sources say.

The strikes come as an alliance of rebel factions led by the Islamist militant organization Hayat Tahrir al-Sham (HTS) has penetrated far into the city, the Britain-based Syrian Observatory for Human Rights said.

Syria's military announced on Saturday that it had made a "temporary troop withdrawal" to prepare a counteroffensive and that dozens of soldiers had been killed in fighting in Aleppo and Idlib in the past few days.

A statement said "armed terrorist organizations" had taken over "large parts" of Aleppo.

Syrian military sources say towns and villages in the surrounding area also came under air attack from Russian and Syrian forces after the rebels carried out their sweep in the region since Wednesday, forcing around 14,000 people to leave their homes, according to the United Nations.

Russian forces have been fighting at the side of troops loyal to Syrian President Bashar Assad since September 2015 in a bid to quell an uprising by an assortment of rebel forces that followed a government crackdown on mostly peaceful pro-democracy protests in 2011.

Significant escalation

The recent eruption of fighting comes after a period in which Syria's civil war was seen to have been widely contained.

Assad, with the help of his allies Russia and Iran, has succeeded in bringing some two-thirds of the country back under government control in the past few years, with Idlib, southwest of Aleppo, remaining as the last rebel stronghold. 

According to Observatory director Rami Abdel Rahman, the rebels took control of most parts of Aleppo without any major resistance on the part of government forces, who have reportedly withdrawn to a suburb. 

"There has been no fighting, not a single shot was fired, as regime forces withdrew," he told the AFP news agency.

The Observatory said 301 people had been killed in fighting, including 28 civilians.

  

The rebels say the offensive comes in response to recent artillery shelling by government forces targeting civilian areas. 

HTS, considered one of the most powerful armed militias in northwestern Syria, is led by al-Qaeda's former Syria branch.

It controls large areas of the Idlib region, as well as parts of neighboring Aleppo, Hama and Latakia provinces.

 tj/wmr (AFP, Reuters, dpa)