BEIRUT - Heavy fighting gripped a flashpoint region near Syria's capital on Sunday, leaving seven civilians dead and threatening a nationwide truce designed to pave the way towards peace talks.

Further east, Syrian government troops lost ground to a brutal assault by the Islamic State group near the key Deir Ezzor military airport.

The escalating violence across Syria in recent days augurs ill for peace negotiations in Kazakhstan later this month. In the Wadi Barada region northwest of Damascus, fresh clashes broke out between rebel groups and advancing government forces, the Syrian Observatory for Human Rights said.

Regime shelling of the Deir Qanun village killed seven civilians and wounded at least 20 other people, the Britain-based monitor said.

Observatory head Rami Abdel Rahman said it was the "highest toll" there since the nationwide truce came into force on December 30. Omar al-Shami, spokesman for the Wadi Barada Media Committee, told AFP shells struck a temporary shelter where displaced women and children had been seeking refuge. The activist group published gruesome pictures of what it said was the aftermath of the attack, including photographs of blood-stained floors and body parts wrapped in blankets.

Fighting has persisted for weeks in Wadi Barada, which is the main source of water for the capital.

Local officials struck a truce with Syrian authorities on Friday to allow maintenance teams into Wadi Barada to restore water to Damascus, but the deal was called off after chief negotiator Ahmed al-Ghadban was killed the next day. The two sides accused each other of assassinating the retired army officer, who had only assumed his duties to restore the water supply on Saturday.

 

"The agreement was considered null this morning after the regime's multiple violations and especially after the killing of the negotiations official," Shami said. Shami told AFP the government's maintenance workers left Wadi Barada without completing the repairs, leaving 5.5 million in Damascus and its suburbs without water.

An official from Syria's reconciliation ministry earlier told AFP the local deal in Wadi Barada "had not completely collapsed". "We are communicating and pursuing new efforts in parallel with the ongoing military action," the official said. Many of Syria's battlefronts have quieted since the entry into force of the nationwide ceasefire brokered by regime backer Russia and opposition ally Turkey.

The deal excludes IS and its militant rival, the Fateh al-Sham Front -- formerly known as Al-Nusra Front.

On Sunday, IS fighters edged closer to the key Deir Ezzor military airport, despite heavy air strikes by government warplanes.

The Observatory said the raids on Sunday killed five civilians, including two women and two children, in Deir Ezzor. It was the second day of the militant group's brutal assault on regime-held territory around the city, the capital of the oil-rich province by the same name.

The fresh advance came "despite more than 120 air strikes carried out by regime forces on militant positions since Saturday morning, in addition to heavy artillery fire," said Abdel Rahman.

IS unleashed a wave of tunnel bombs and suicide attackers against government forces on Saturday, leaving 12 government fighters dead.

Another 20 IS militants were killed in the clashes.

The extremist group has lost swathes of territory in northern Syria to Kurdish fighters as well as to a Turkish-backed rebel alliance, but it remains on the offensive in other parts of the country.

In addition to its push in Deir Ezzor, IS recently recaptured Palmyra in central Syria from government forces.

The conflict began with protests against the rule of President Bashar al-Assad in 2011 but has since morphed into a multi-front war.

Although they support opposing sides in Syria's war, Moscow and Ankara have worked closely to negotiate the nationwide truce and to prepare talks in the Kazakh capital Astana on January 23.

US president-elect Donald Trump's transition team has been invited to take part in the talks, but has not yet officially responded.

Attendance by the new president's team would be a strong signal of Trump's determination to improve relations with Russia.