BEIRUT (Reuters) - A rebel group fighting under the Free Syrian Army banner in northwest Syria has withdrawn from a shaky nationwide ceasefire, blaming the government and its allies for violations.

Rebels drive their vehicles on the outskirts of the northern Syrian town of al-Bab, Syria January 29, 2017. REUTERS/Khalil Ashawi

“Due to Russia’s lack of commitment as a guarantor...we announce that, as of today, we are not bound by this agreement,” Jaish al-Ezza, a signatory to the deal brokered by Russia and Turkey, said in a statement on Sunday.

The group said its decision was in response to what it described as heavy Russian bombardment of its positions and surrounding areas in Hama province.

Fighting and air strikes have plagued the ceasefire between the government and rebel groups since it took effect in late December, with the combatants accusing each other of violations.

After two days of negotiations in Kazakhstan last week, Russia, Turkey, and Iran agreed to ensure full compliance with the fragile truce.

Jaish al Ezza, which has received foreign aid from states opposed to Syrian President Bashar al-Assad, also blamed government forces and allied militia for breaching the ceasefire in Wadi Barada near Damascus.

A month-long offensive against rebels in Wadi Barada ended on Sunday when the government captured the valley, where a major spring supplies most of the capital’s water.

The Hama-based rebel group’s withdrawal from the truce could further complicate the battlefield in the insurgent-held northwestern corner of Syria, where jihadists and more moderate Islamist factions are at war with each other.

The Syrian conflict pits Assad’s government, backed by Russia and Iran, against an array of mostly Sunni rebel groups, including some supported by Turkey, Gulf monarchies, and the United States.

Despite an overall reduction in violence, more than 400 civilians have died in clashes and bombardment since the truce began, the Syrian Observatory for Human Rights war monitor said.