BEIRUT

Intense clashes in southern Syria have killed scores of pro-government and insurgent fighters in the past week, a group monitoring Syria's war has said as it forecast even fiercer violence as the weather clears.

Syria's army and allied combatants from Lebanon's Hezbollah 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.