"Four Al-Nusra Front fighters carried out suicide attacks this morning, driving vehicles packed with explosives into four regime forces' checkpoints in the Jabal al-Arbaeen area near Ariha city," said the Syrian Observatory for Human Rights.
The Britain-based group said that dozens of troops were killed or wounded, without giving specific figures.
Fierce fighting broke out in the area, pitting army troops backed by pro-regime militia against rebels and jihadists, said the Observatory.
The army controls the cities of Idlib and Ariha in Idlib province of northwest Syria, but much of the countryside is under rebel control.
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Ariha lies on the road from Idlib to Latakia on the Mediterranean coast, the heartland of President Bashar al-Assad's regime and his Alawite offshoot of Shia Islam.
Like the majority of Syria's population, most of the rebels are Sunni Muslims.
The rebels are "determined to cut off the road before the presidential vote" on June 3 that is to be contested only in regime-controlled areas, according to the Observatory.
Syria's three-year war broke out as Arab Spring-inspired demands for political change, but it morphed into an insurgency after Assad's regime unleashed a brutal crackdown on dissent.
The war has killed more than 160,000 people, the Observatory estimates, and forced nearly half the population of Syria to flee their homes.