Syrian government forces, backed by Russian air strikes, broke through rebel lines near Aleppo just days after U.N.-backed peace talks were put on hold. (Reuters)

Syrian rebels battled for their survival in and around Syria’s northern city of Aleppo on Thursday after a blitz of Russian airstrikes helped government loyalists sever a vital supply route and sent a new surge of refugees fleeing toward the border with Turkey.

The Russian-backed onslaught against rebel positions in Aleppo coincided with the failure of peace talks in Geneva, and helped reinforce opposition suspicions that Russia and its Syrian government allies are more interested in securing a military victory over the rebels than negotiating a settlement.

After two days of what rebel fighters described as the most intense airstrikes yet, government forces had succeeded on Wednesday in cutting off the rebels’ main supply route from the Turkish border to the portion of Aleppo city that remains under opposition control. On Thursday, the government captured several more villages in the surrounding countryside, prompting fears among residents and rebels that the city could soon be entirely surrounded.

The loss of Aleppo, Syria’s largest city and the most significant urban center to fall, at least partially, under rebel control, would represent a potentially decisive blow to the nearly five-year-old rebellion against Syrian President Bashar al-Assad. The rebels have maintained control of much of Aleppo since they surged into the city in 2012, prompting U.S. intelligence assessments that they eventually would topple the government in Damascus.

Instead, Russia and Iran stepped up their assistance to the Assad regime, helping the government stem, then steadily reverse, the losses. Most of the pro-government forces now fighting in northern Aleppo province are Shiite militias from either Iraq or Afghanistan that have been recruited by Iran to help out its ally in Damascus, according to rebels and military analysts. The intervention by the Russian air force, ostensibly intended to battle the Islamic State, has mostly targeted moderate rebels, tilting the military balance in favor of Assad and enabling the government’s spurt of gains in recent weeks.

Residents inspect damage in the rebel-held al-Shaar neighborhood of Aleppo after airstrikes by pro-Syrian government forces. (Abdalrhman Ismail/Reuters)

With the push around Aleppo, pro-government forces were able to break a rebel siege on two predominantly Shiite villages, Nubl and Zahra, which had been surrounded by rebel forces for the past three years and sustained only by government airdrops of food.

In its determination to see the peace talks get underway, the United States had pressured the rebels’ allies, including Turkey and Saudi Arabia, to curtail supplies of weapons, leaving the rebels vulnerable to the new offensive, according to rebel commanders.

This latest battle also has the potential to trigger a major new humanitarian crisis. The United Nations’ inability to deliver aid to towns besieged by government forces had emerged as a major obstacle in the stalled talks. With rebel-held Aleppo almost entirely surrounded, there is a risk that hundreds of thousands of people living there soon could be cut off entirely. Aid agencies said the airstrikes have forced an almost total suspension of aid deliveries across the Turkish border.

“Opposition forces are losing ground by the minute. We’re looking at a nightmare humanitarian situation,” said Rae McGrath, director of operations in northern Syria and Turkey for the aid agency Mercy Corps.

“There are a lot of people on the move,” he said. “This is certainly the worst situation we’ve seen since the beginning of the war.”

Rebel fighters sounded desperate as they described enduring more than 200 airstrikes in the past 24 hours alone. Commanders from a range of rebel groups, from moderates to the al-Qaeda-affiliated Jabhat al-Nusra, issued urgent appeals for reinforcements from other parts of the country.

After days of mediated talks to end the war in Syria, U.N. envoy Staffan de Mistura has called for a temporary pause until Feb. 25. (Reuters)

“We are fighting our most important battle yet. We are fighting to prevent a regime siege on Aleppo,” said Abdul Salam Abdul Razzak, a spokesman for the Noureddin al-Zinki rebel movement, reached by telephone on the northern outskirts of Aleppo.

“In the coming days, the battle will be fierce. We will keep fighting till the last fighter, and we hope we will not let our people down.”

Speaking in London at an international conference to secure donations to aid Syrians inside and outside the country, Turkish Prime Minister Ahmet Davutoglu said that some 70,000 civilians were streaming toward Turkey’s borders to escape the offensive.

Aid agencies said at least 10,000 had gathered along Syria’s northern border with Turkey. But Turkey, which is already hosting about 2.5 million refugees and has come under pressure from the international community to halt the flow of foreign fighters, has kept its borders sealed shut to new refugee arrivals for the past year. Videos posted by activists on social media showed thousands of people clutching their possessions as they walked toward the Syrian side of the border crossing of Bab al-Salameh, but they were not allowed to cross into Turkey.

The fall of Aleppo to the government would present a major challenge to Turkey and Saudi Arabia, the rebels’ staunchest supporters, but it was unclear what, if anything, they could do to prevent it.

Turkish troops have in recent months reinforced their presence along their country’s border with Syria, and Russian Defense Ministry spokesman Igor Konashenkov told reporters in Moscow that Russia suspected Turkey was preparing to take military action in Syria.

But Turkey has had limited room to maneuver in Syria since it shot down a Russian jet that had strayed briefly into Turkish airspace in December, triggering retaliatory measures by Russia.

The talks in Geneva were suspended Wednesday by Staffan de Mistura, the U.N. special envoy for Syria, who cited the government’s refusal to submit to opposition demands for the implementation of U.N. resolutions calling for a halt to the airstrikes and the delivery of aid to besieged areas.

The talks also snagged on disputes over whom to define as a “terrorist” on the complicated Syrian battlefield. The Syrian government regards all those fighting Assad, including moderate rebels backed by the United States, as terrorists and has said it will not negotiate with the rebel groups that were represented in the opposition delegation to Geneva.

Separately, a spokesman for Saudi Arabia’s military told the Saudi-owned al-Arabiya TV network that his country was prepared to send troops to join the fight against the Islamic State. But it was unclear in what capacity or where the Saudi government envisaged deploying such troops.

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