Meanwhile, UN Secretary-General Antonio Guterres has called for an end to fighting in northwestern Syria, where hundreds of combatants reportedly died this week as regime forces advanced on a rebel-held town.
Syrian insurgents carried out two suicide car bomb attacks in an assault on pro-regime forces in Aleppo on Saturday and opened a new front northeast of the city, an attempted fightback after territorial gains for regime leader Bashar al Assad.
Backed by Russian air power, Syrian regime forces had made a significant advance into the rebel-held northwest this week, seizing the town of Maarat al Numan, part of an offensive to secure the main highway between Damascus and Aleppo.
The suicide attacks were carried out by militant group Hayat Tahrir al Sham and targeted the Jamiyat al Zahraa area on the western edge of Aleppo. A third car bomb was set off by remote control, a source with the group said.
A news outlet linked to the group, Ebaa, published a video which it said showed elite Tahrir al Sham fighters pledging "allegiance to death and jihad" before the attack on Jamiyat al Zahraa, watched by the group's leader, Abu Mohammad al Jolani.
The northwestern corner of Syria including Idlib province and adjoining areas of Aleppo is the last major rebel foothold in Syria, where the regime has taken back most of the ground once held by its enemies with Russian and Iranian support.
Syrian news agency SANA said regime's troops had destroyed four car bombs before they reached their targets in that area. Syrian regime forces were firing rockets and artillery at militant groups on the Jamiyat al-Zahraa front, it said. Militants had also fired rockets at residential districts of Aleppo.
UN chief calls for end to escalating conflict
UN Secretary-General Antonio Guterres on Saturday called for an end to fighting in northwestern Syria, where hundreds of combatants reportedly died this week as regime forces advanced on a rebel-held town.
Syria's Russian-backed forces are advancing on the rebel-held town of Saraqeb amid a double-pronged push into Idlib province, home to some three million people, half of whom have been displaced from other parts of the country.
"The Secretary-General is deeply concerned by the ongoing military escalation in northwest Syria and calls for an immediate cessation of hostilities, " his spokesman said.
"He reaffirms that attacks on civilians and civilian infrastructure, including on healthcare and educational facilities, are unacceptable."
The fighting in Idlib and in western Aleppo over the past week has killed 205 pro-regime forces and 220 anti-regime combatants, the Syrian Observatory for Human Rights said.
Thousands of refugees headed toward Turkey
In northwest Syria, thousands of people continue to move towards the border with Turkey, fleeing ongoing attacks by the regime and its ally Russia .
According to reports on Saturday evening, the main road leading to the Turkish border was congested with vehicles full of people trying to reach safety.
UNICEF said Saturday that violence this week forced 6,500 children to flee daily, bringing the total number of displaced children in northwest Syria to more than 300,000 since early December.
The regime, which controls more than 70 percent of Syria, has repeatedly vowed to reclaim the entire country, including Idlib.