Syria's army is preparing to assault a key rebel bastion near Damascus, a pro-regime newspaper said Thursday, as activists reported heavy shelling and fighting in the area.

"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 Qalamun mountains, Al-Watan reported.

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

"Every day there is progress" by the army, said the newspaper, adding that rebels had been using the two hills as supply routes.

Regime forces backed by fighters of Lebanon's Shiite Hezbollah launched an offensive in the Qalamun area in November.

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

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

It reported fighting between rebels and troops and Hezbollah fighters on the outskirts of Yabrud on Thursday.

"Last night, the shelling was very fierce," Amer, an activist in the Qalamun area, told AFP via Skype.

Amer said he was confident rebels could defend the town against a ground offensive, but said most residents had fled.

Yabrud was once home to some 50,000 people. Last week, the United Nations refugee agency UNHCR said some 13,000 had crossed from Qalamun into Lebanon's border town of Arsal.

Elsewhere in Syria, five people were killed and 13 wounded in a mortar attack "by terrorists" on the regime-held Akrameh district of Homs city, state television said, 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.

The Observatory said Wednesday saw the highest death toll among rebels, jihadists and loyalists since the start of Syria's conflict in March 2011.

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.

Meanwhile, in northern Syria's Hasake province, home to the majority of the country's Kurds, jihadists destroyed a Sufi Muslim shrine as they advanced on Tal Maaruf village, residents said.

Islamic State of Iraq and the Levant (ISIL) militants "blew up the shrine, and burned a mosque and a police station," said Massoud Akko, a Kurdish journalist and native of Hasake province, citing residents.

ISIL follow an extremely strict interpretation of Islam which views Sufi Muslims as heretics.

Syria's 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.