Syrians fleeing the embattled northern province of Aleppo walk toward the frontier post of Bab al-Salameh bordering Turkey on February 5, 2016. (AFP/Getty Images)

Thousands of people fleeing a Russian-backed offensive in the northern Syrian province of Aleppo were blocked from entering Turkey on Friday amid fears of a fresh influx of refugees.

The potential new exodus from Syria began earlier this week after Syrian government loyalists backed by Russian airstrikes launched a major offensive that severed the main rebel supply line leading south from Turkey to the rebel-held portion of the city of Aleppo.

The battles prompted tens of thousands of people to flee their homes, most of them to escape intense airstrikes that have reduced entire villages to rubble, according to rebel fighters and activists in the area.

The fighting continued to rage Friday, with the rebels pushing back against government attempts to capture more territory in the northern Aleppo countryside that has been the main focus of the battle. The boom of distant airstrikes echoed at regular intervals through the mostly deserted border crossing at Kilis on the Turkish side of the border.

Aid agencies and the Turkish government say 70,000 to 100,000 people may have been newly displaced and are on the move seeking safety inside northern Syria.

At least 20,000 of them are camped out at the Bab al-Salameh border crossing on the other side of the fence from Kilis, according to the United Nations. Most come from the areas nearest to the front lines in northern Aleppo.

Turkey, which is hosting more than 2.5 million Syrian refugees, has kept its border mostly shut to new arrivals for more than a year. It is now under even more pressure to continue to do so from European countries anxious over the influx of refugees and migrants to Europe.

In keeping with that policy, a Turkish aid agency erected tents and distributed food on the Syrian side of the border, said Majid Najar, a Syrian activist helping with the aid effort in Bab al-Salameh. “People are still coming, and the numbers are increasing,” he said, speaking by telephone.

The numbers could swell dramatically if the Syrian government succeeds in its apparent goal of encircling the rebel-held portion of the city of Aleppo, where an estimated 300,000 people are living, according to the United Nations. Although the road north to Turkey has been cut, Aleppo residents still have an escape route — and rebels, a supply line — to the west, via the border crossing of Bab al-Hawa.

Residents of Aleppo city have mostly stayed put for now because they know that they will be prevented from entering Turkey, said Ameen al-Halabi, the nom de guerre of an activist living in Aleppo. “If people had guarantees they could enter Turkey, everyone would leave,” he said. “I would leave.”

The surge in fighting contributed to the collapse of peace talks in Geneva this week and has focused growing criticism among Western allies on the role of Russia in fueling a war it had said it was seeking to solve.

“Intense Russian airstrikes, mainly targeting opposition groups in Syria, are undermining the efforts to find a political solution to the conflict,” NATO Secretary General Jens Stoltenberg told reporters in Amsterdam on Friday.

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Today’s coverage from Post correspondents around the world