Pro-Syrian Army Forces, including Lebanon's Shiite Hezbollah movement, had agreed on a 48-hour ceasefire, until dawn on Saturday, in the rebel bastion of Zabadani and the government-held villages of Fuaa and Kafraya.
"The ceasefire has collapsed in Zabadani, Fuaa, and Kafraya this morning," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
A Kafraya resident speaking to AFP by phone said "dozens of shells have fallen on the town since early morning."
In Return Syrian Army shelling terrorist position in Zabadani.
Fuaa and Kafraya villages in Syria's northwest Idlib province, have been surrounded by a terrorist alliance including Al-Qaeda's affiliate Al-Nusra Front.
Syrian army wants to reach a broader deal including rebel fighters leaving Zabadani and the evacuation of civilians from Fuaa and Kafraya. But the talks failed overnight.
The resumption of war was confirmed by Mohammad Abu Qassem, secretary general of Syria's Tadamun (Solidarity) Party and a mediator of the truce.
"The truce has ended, the negotiations have failed, and military operations have resumed in Zabadani, Fuaa, and Kafraya," he told AFP.
This marks the second time a local ceasefire has collapsed for the three towns this month.
The first ceasefire began on August 12 as a 48-hour truce and was extended for another day as negotiators tried but also ultimately failed to reach a broad deal.