DAMASCUS (AFP) ― Syrian troops advanced Saturday in the key rebel bastion of Yabrud as the country’s civil war entered its fourth year, with more than 146,000 dead, millions displaced and peace efforts stalled.

The Syrian Observatory for Human Rights NGO said army forces were advancing with support from Lebanon’s Shiite movement Hezbollah, a staunch regime ally.

A military source said “13 rebel chiefs leading operations are dead,” adding there were “many deaths among the insurgents.”

State television broadcast images of the town from its outskirts and said troops had advanced 2 kilometers inside the town towards a roundabout.

Yabrud is a key rebel supply route and their last stronghold in the Qalamun region along the border with Lebanon and on the highway between Damascus and third city Homs.

The latest battle illustrates the intractability of the conflict that began on March 15, 2011, after popular uprisings that toppled dictators in Tunisia and Egypt.

Protests erupted in Syria’s southern city of Daraa after teenagers were arrested over graffiti declaring: “The people want the fall of the regime.”

President Bashar al-Assad’s regime cracked down on the protests, civilians took up arms, soldiers began to desert and an insurgency became full-scale civil war after the regime bombed the central city of Homs in February 2012.

Two years later, the conflict appears to have reached stalemate, with some predicting it could last another 10 or 15 years.

Rebels control large swathes of Syria, but are fighting both the regime and an al-Qaida-inspired group they once welcomed.

Loyalist forces hold the more densely populated regions, and are advancing south of Damascus, in the Qalamun region and in Aleppo in the north, seeking to protect the coast, major towns and key roads.

Syria’s mostly exiled political opposition has secured Western recognition but is largely ignored by rebels on the ground.