Jihadists from the Islamic State group pressed their campaign Friday to capture Hasakeh, a provincial capital in northeast Syria, in fierce battles with government forces backed by air strikes.
"Fierce clashes continued Friday between regime forces and IS south of Hasakeh city. The regime is violently and intensely bombarding jihadist positions from the air," the Syrian Observatory for Human Rights said.
The Britain-based monitor said the regime was using barrel bombs -- large containers packed with explosives that are dropped from helicopters -- against jihadists edging towards the city, which is divided between Kurdish and government control.
Since their offensive began on Saturday, IS fighters have advanced to the southern outskirts of Hasakeh with the aid of suicide attacks and heavy mortar fire.
Citing a military source, Syria's state news agency SANA said the army had used "aerial weapons... to destroy equipment belonging to the IS terrorists".
The assault has killed at least 71 loyalists and 59 extremists, including 11 who targeted regime positions with car bombs, IS's signature weapon, the Observatory said.
The jihadists, who have expanded their control in central and eastern Syria and in neighbouring Iraq, seized a number of key posts, including a prison and power plant.
Hasakeh has since been left without power, local activist Arin Shekhmos told AFP.
Kurdish militia, locked in battles with IS in other parts of Hasakeh province, have yet to take part in the clashes south of the city.
"For the moment, the Kurds are not taking part in the fight as the battles have not reached their area," Abdel Rahman said.
A Turkish official said around 4,000 Syrians have sought refuge in Turkey this week, fleeing fresh clashes pitting Kurdish fighters against IS.
Kurdish forces launched an offensive last week against the jihadists in the border province of Raqa.
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- UN 'outrage' over barrel bombs -
In New York, the UN Security Council condemned a recent wave of barrel-bomb attacks in Syria's northern Aleppo province that have left scores dead.
Council members "expressed outrage at all attacks against civilians, as well as indiscriminate attacks, including those involving shelling and aerial bombardment such as the use of barrel bombs".
The United Sates, Britain and France have accused President Bashar al-Assad's forces of using barrel bombs, saying only Damascus has helicopters, but he has repeatedly denied using barrel bombs.
The chief of Lebanon's Shiite militia Hezbollah, Hassan Nasrallah, said Friday his fighters had managed to "liberate dozens of square kilometres" in the Qalamun region straddling the Syrian-Lebanese border, pushing back Al-Nusra Front, Al-Qaeda's affiliate in Syria, and its allies.
And he vowed that Hezbollah will next turn its sights on IS.
"The next battle is in the... parts (of Qalamun), which are controlled by Daesh," he said, using the Arabic acronym for IS.
"Daesh is on our borders," he said, branding the group as a threat to Lebanon's existence.
On Friday, the Syrian army said it had seized numerous villages and strategic hilltops in Qalamun with Hezbollah's help.
In neighbouring Iraq, IS jihadists fired 40 rockets on a residential area near Amriyat al-Fallujah, 30 kilometres (18 miles) southwest of Baghdad and one of the few districts of Anbar province still under government control.
The police chief and a medic at the local centre said six women and four children were wounded in the incident.
IS militants used an unprecedented wave of suicide truck bomb attacks to seize Ramadi, capital of Anbar province, in a three-day blitz last month.
Iraqi Prime Minister Haider al-Abadi, who is to meet US President Barack Obama in Germany at the weekend, has said his forces would retake Ramadi within days but operations have stalled and focused instead on sealing off the city.