Rebel fighters seized control of a key dam on the Euphrates river in northern Syria, limiting the army's overland access to the battleground city of Aleppo to a single route, a monitoring group said on Monday.
"The capture of the Tishrin dam is very important. It means that the army basically has only one road left to Aleppo," said Rami Abdel Rahman, director of the Syrian Observatory for Human Rights.
"The highway crossing over the Tishrin dam was the last main route from Raqa province (northeast) under regime control. Now it is impassable," the head of the monitoring group told AFP by phone.
With the overnight capture, the rebels now hold sway over a wide expanse of territory between the two provinces bordering Turkey which backs the revolt against President Bashar al-Assad.
The other main route from Raqa to Aleppo passing through the town of Al-Thawra further south along the Euphrates is dotted with both regime and rebel checkpoints, Abdel Rahman noted.
He pointed out there is another small bridge to the north of Tishrin dam but the road is winding and difficult.
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The army must now rely on the Damascus-Aleppo highway to bring men and equipment to Syria's embattled commercial hub, where fighting is at a stalemate after months of deadly urban combat.
"The stretch from Damascus to Maaret al-Numan is government-held," said Abdel Rahman. "The rebels control Maaret al-Numan, though not the highway that passes alongside it. From there to Aleppo, no one is in control."
The regime also has a parallel military road at its disposal, but this is a rugged and challenging route, Abdel Rahman said. "If the main road takes you 10 hours, this will take four times as long."
Videos posted on the Internet show about a dozen rebel fighters in military fatigues walking at night on a road crossing the Tishrin dam.
The strategic advance came after several days of clashes and a siege of the dam by the insurgents, according to the Observatory and residents, with the military responding with air strikes.
Elsewhere on Monday, fighting erupted along the ceasefire line of the Golan Heights, with two rebels killed in Al-Buraykah and Bir Ajam, both villages inside the Syrian section of a demilitarised zone, the Observatory said.
Israel's military earlier reported that gunfire on Sunday night from Syria hit the Israeli-occupied Golan Heights close to a military vehicle monitoring the ceasefire line but causing no injuries.
The Observatory, which relies on a network of activists and medics on the ground for its information, recorded an initial toll of 14 people killed nationwide Monday, after recording 119 deaths on Sunday: 43 civilians, 35 rebels and 41 soldiers.