Intense clashes in southern Syria have killed scores of pro-government and insurgent fighters in the past week, a group monitoring Syria’s war said yesterday, forecasting even fiercer violence to come as the weather clears.

Syria’s army and allied combatants from Lebanon’s Hizbollah launched a large-scale offensive in the region last week against insurgent groups including al Qaeda’s Syria wing Nusra Front and non-jihadist rebels.

The battle is significant because it is one of the last areas where mainstream rebels opposing President Bashar al-Assad have a foothold. Such groups have lost ground to hardline Islamist militants in the four-year conflict.

More than 50 rebels have been killed in the fighting, the head of the Britain-based Syrian Observatory for Human Rights said.

Rami Abdulrahman said 43 members of the Syrian army and allied groups had also died, including 12 officers.

“Now the weather is better there will be Syrian air strikes. With the air strikes they will move forward,” he said.

Syrian state media and Hizbollah’s al-Manar channel have reported on the battles in the south during the week, saying the army had been reclaiming territory from “terrorists”. State media have said that a number of enemy fighters had been killed. Syrian officials were not available for comment yesterday. Abdulrahman, who tracks the war using sources on the ground, said around 5,000 pro-government troops were taking part in the offensive which aims to take a triangle of rebel-held land from rural areas southwest of Damascus to Deraa city to Quneitra.

He said there were reports that 10 members on the government side had been executed after being accused of passing information to the enemy.

He also said Nusra Front fighters had been killed in battles but exact numbers were not yet known.

Winter weather had limited fighting in the past few days and prevented air strikes, one of the army’s most potent weapons against insurgents.

Abdulrahman said the army and allied groups planned to eventually involve 10,000 fighters in the offensive.

The southern rebels, often described as the best organised of the mainstream armed opposition, see themselves as the last hope for a conflict dominated by Islamist militants.

They have been seeking a higher profile and more aid.

But Nusra Front also has a presence in the region, complicating their efforts. Sunni Islamist insurgents including the ultra hardline Islamic State also control wide expanses of Syria’s north and east.