BEIRUT — Syria’s army is preparing an assault on a key rebel bastion near Damascus, a pro-regime newspaper said Thursday, as the opposition reported a “massacre” of civilians near Damascus.

“The Syrian army is preparing to launch a new phase” on the town of Yabrud near the border with Lebanon in its offensive in the Qalamoun mountains, Al-Watan reported.

It said troops loyal to President Bashar Assad have seized control of two strategic hills near Yabroud, which has been the target of heavy air raids and tank fire since early February.

The Qalamoun region is a main rebel supply route for weapons and fighters from neighboring Lebanon. Regime forces backed by fighters of Lebanon’s Shiite movement Hezbollah launched an offensive in the area in November.

They have expelled rebels from several strategic towns, but Yabroud — the largest in the region — has so far remained an opposition stronghold.

‘Civilian massacre’

Thursday’s developments come a day after the heaviest death toll among fighters on both sides of the conflict in three years, according to the Syrian Observatory for Human Rights.

The group, which relies on activists and doctors on the ground for its information, said 326 fighters were killed nationwide.

They included 242 opposition fighters, among them at least 33 jihadists. Another 84 were loyalists, including 37 paramilitaries and non-Syrian fighters.

But Monzer Aqbiq, a senior adviser to opposition leader Ahmad Jarba, disputed claims by state media that government troops had ambushed and killed more than 170 Islamist rebels near Damascus on Wednesday.

“This was a civilian bloodbath committed by the regime and Hezbollah forces,” he said.

He said “110 desperate and starving people were trying to escape Eastern Ghouta for medical treatment” and that “some fighters were escorting the civilians for protection as they tried to escape the siege.”

Aqbiq said the group, which included wounded civilians, was ambushed and “massacred in cold blood”.

State television, meanwhile, said five people were killed and 13 wounded in a mortar attack “by terrorists” on the regime-held Akrameh district of Homs city, using the regime’s term for rebels.

Akrameh borders a handful of rebel-held districts in the heart of Homs that have been under choking army siege for more than a year and a half.

Syria’s three-year war has killed more than 140,000 people, the Observatory says, and forced millions more to flee their homes.

On the humanitarian front, the UN agency for Palestinian refugees UNHCR said it distributed 450 food parcels in the Palestinian refugee camp of Yarmuk in Damascus on Wednesday.

UNRWA chief Filippo Grandi on Tuesday said the situation in Yarmuk was “shocking” and called for sustained access for aid deliveries to some 18,000 Palestinians trapped there under fire.

The Associated Press contributed to this report.