BEIRUT: A brief truce between Syrian regime forces and rebel groups in three key towns ended early Saturday as the warring parties resumed clashes and shelling, a monitoring group said.

Pro-regime forces, including Lebanon's Hezbollah militia, 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.

"There are clashes and shelling in Zabadani, and opposition fighters are shelling Fuaa and Kafraya," he told AFP.

But he had no details on who initially began firing and whether there were any casualties.

Fuaa and Kafraya, the last two regime-held villages in Syria's northwest Idlib province, have been surrounded by a rebel alliance including Al-Qaeda's affiliate Al-Nusra Front.

The siege came in retaliation for a fierce offensive on Zabadani, along Syria's border with Lebanon, by pro-regime forces early last month.

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 ultimately failed to reach a broad deal.

The earlier talks faltered before reaching an agreement on the withdrawal of fighters from Zabadani and the evacuation of civilians from Fuaa and Kafraya.

The rebels have also sought the release of prisoners held by the regime.

The same points were being discussed during the second brief ceasefire, but the warring parties were not able to reach an agreement, Abdel Rahman said.

More than 240,000 people have been killed since Syria's conflict began in March 2011, and half of the country's population has been displaced by the war.