BEIRUT (Reuters) - The death toll from air strikes on a Syrian town in a “de-escalation zone” has risen to 61, a war monitor said on Tuesday, a demonstration of the fragile state of areas set up in attempt to ease the violence.

Jihadist rebels blamed Russian warplanes of carrying out Monday’s attack and said they would fight back against Syrian President Bashar al-Assad’s forces and his Russian and Iranian backers in the six-year-old conflict.

The British-based Syrian Observatory for Human Rights said three air strikes hit the market in Atareb, west of Aleppo,

and killed at least 61 people.

Atareb is inside what is known as a de-escalation zone under an agreement between Turkey, Russia and Iran to reduce the bloodshed. But despite the diplomatic efforts, fighting continues in many areas, including Aleppo, Idlib, Raqqa, Deir al-Zor and Hama.

“(The zones) did de-escalate fighting,” U.N. humanitarian adviser Jan Egeland told Reuters. But lately, “there has been increased fighting also.”

The zones were set up under the Astana process, a series of talks in the capital of Kazakhstan between Russia and Iran, and the rebels’ supporter Turkey.

They agreed in September to deploy observers on the edge of a de-escalation zone in Syria’s Idlib province, which is largely under the control of Islamist insurgents.

Following the air strikes, the Tahrir al-Sham jihadist alliance denounced the ceasefire talks and pledged to keep fighting government forces and their Russian and Iranian allies.

“This aggression and crimes confirms for us that there is no solution with the colonizers without fighting and struggling,” it said.

Tahrir al-Sham includes the group formerly known as the Nusra Front, which changed its name last year when it broke formal ties to al Qaeda.