Forces loyal to Syria’s President Bashar al-Assad carry their national flag as they walk along a street in Qusair, in this handout photograph distributed by Syria’s national news agency SANA on Wednesday. Syrian forces and their Hezbollah militant allies seized control on Wednesday of the border town of Qusair, dealing a strategic defeat to rebel fighters battling for two years to overthrow President Bashar al-Assad. Image Credit: Reuters

London: The Syrian border town of Qusayr has fallen to Hezbollah forces after a three-week siege that pitched the powerful Lebanese Shia militia against several thousand Sunni rebels in what had been billed as a defining battle of the civil war.

Rebel groups released a statement early on Wednesday confirming that they had pulled out of the strategic town in the early hours. Rebel fighters are believed to have taken refuge in hamlets near Syria’s third city, Homs, around 30km to the north.

Outgunned since the siege began, rebels inside the town said they had no option but to flee “in face of this huge arsenal and lack of supplies and the blatant intervention of Hezbollah”.

“Dozens of fighters stayed behind and ensured the withdrawal of their comrades along with the civilians,” the statement said.

The fate of residents who remained as the battle raged remains unclear. Rebel leaders from the town who contacted the Guardian earlier this week said more than 15,000 people had stayed in their homes from a pre-war population of around 30,000.

Qusayr had been heavily bombed by artillery and shells dropped by the Syrian air force and rebel supply lines had been severed by regime forces to the north and east and Hezbollah advances from the south and west.

Hezbollah has led the attack. Its large-scale public role has drawn strident criticism in Lebanon and across the Sunni Arab world, where inter-Muslim sectarian tensions have reached dangerous highs, especially since the assault on Qusayr began.

There was no immediate reaction from the Hezbollah leadership. However, media outlets loyal to the group announced that the town had been “cleared of terrorists” at around 6.30am on Wednesday. Hezbollah is believed to have suffered close to 200 casualties during the fighting, a higher number than its members had expected before launching the attack.

Shia residents of the south Beirut suburb of Dahiyah were on Wednesday handing out celebratory sweets at traffic lights to mark the group’s victory in Syria — a battlefield far from southern Lebanon, where it has battled its traditional foe, Israel, for much of the past 30 years.

Hezbollah’s role as a spearhead against a Sunni insurgency in an Arab land has meant a rethink of the group’s raison d’etre and has unambiguously wedded it to the fortunes of the Al Assad regime, whose military had been unable to gain ground in numerous battles across the country until the increased role of Hezbollah and a militia of Shia fighters from Syria and elsewhere, known as Abu Fadl Al Abbas.

Iran, the main patron of both groups, released a statement on Wednesday morning “congratulating the Syrian people for their victory”.

In recent days Hezbollah had deployed hundreds of its elite forces to Qusayr, a sign that the battle was drawing to a close despite resistance from rebels who had proved tougher than expected. The defence of the town was primarily led by homegrown fighters, among them defectors. However, reinforcements from Homs and Aleppo, as well as a contingent of around 200 from the Al Qaida-aligned Jabhat Al Nusra, arrived one week ago. The total number of fighters is thought to have been around 3,000.

Rebel casualties are unknown. But on Monday, a surgeon from the town contacted the Guardian to say that his supplies of essential medicines had run out. “We have had no resupplies at all,” he said. “Nothing has been able to get through.”

Qusayr had been hailed as a key strategic route for both sides. Located roughly halfway between Damascus and Homs, it is situated on a crucial supply line for the regime, which had for much of the past year been unable to secure the road between Syria’s first and third cities.

The majority Sunni town also stands incongruously between the Shia villages of northern Lebanon and along the border itself and Syria’s Alawite heartland, which spreads from near Homs north-west to the Mediterranean cities of Latakia and Tartous.

Maintaining a contiguous link between the areas is believed to have been a military goal for regime officials in the event that the war leads to a breakdown of borders in the region and a need to consolidate a safe zone for Alawites and Shia populations.

Buoyed by victory in Qusayr, a broader role for Hezbollah is now thought to be on the agenda. Unconfirmed reports in recent days have suggested that the group will now be moved to Aleppo in similarly large numbers, where it will attempt to dislodge rebel groups who have controlled 60 per cent of Syria’s largest city for the past 10 months.