Syria's Al-Qaeda branch staged four suicide bomb attacks on army positions Sunday, leaving dozens of casualties, in a bid to cut off Idlib province from the coast, a monitoring group said.
The attacks came a day after the Al-Nusra Front announced the creation of an arms factory.
"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 air force also struck the area, killing two rebels and wounding another 15, it added.
The army controls the cities of Idlib and Ariha in Idlib province of northwest Syria, but much of the countryside is under rebel control.
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.
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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.
The opposition and its Western backers have condemned as a "farce" the election in which Assad is expected to stroll to victory.
The attacks came a day after the jihadists announced via Twitter that they had launched a project to manufacture weapons, and called on "all Muslims" to support it.
"In a bid to create a full-scale military industry... Al-Nusra Front has established the Bas (courage) institution for military production and development, the first fully jihadist project of development and fabrication of effective weaponry."
Al-Nusra Front said it was "an opportunity to serve jihad and jihadists".
Syria's war broke out in March 2011 as Arab Spring-inspired demands for political change morphed into an insurgency after Assad's regime unleashed a brutal crackdown on dissent.
Al-Nusra Front surfaced in the conflict in 2012.
The war has killed more than 160,000 people, the Observatory estimates, and forced nearly half the population of Syria to flee their homes.