Aid agencies are warning of a worsening humanitarian crisis in northern Syria as sharply intensified Russian airstrikes paralyze aid supply routes, knock out bakeries and hospitals and kill and maim civilians in growing numbers.

Air attacks have escalated significantly since Turkey shot down a Russian warplane along the Turkey-Syria border on Nov. 24, the aid agencies say, with Russia responding to the incident by stepping up its effort to crush the anti-government rebellion in the insurgent-held provinces bordering Turkey.

Among the targets that have been hit are the border crossings and highways used to deliver humanitarian supplies from Turkey, forcing many aid agencies to halt or curtail their aid operations and deepening the misery for millions of people living in the affected areas, according to a report this month by the U.N. Office for the Coordination of Humanitarian Affairs.

Hospitals and health facilities also have been struck, reducing the availability of medical care for those injured in the bombings. According to the U.N. report, at least 20 medical facilities have been hit nationwide in Syria since Russia launched its air war on Sept. 30.

“This is an emerging humanitarian crisis. There is extreme suffering, and people are not being protected,” said Rae McGrath, country director for Turkey and North Syria for the American aid agency Mercy Corps, one of the largest providers of food aid in northern Syria. Since the Russian strikes began, the agency has been able to deliver only a fifth of the amount it normally provides, he said.

An injured Syrian man is carried on a stretcher at a field hospital to receive treatment following reported airstrikes by regime forces on the town of al-Nashabiyah in the eastern Ghouta region, a rebel stronghold east of the capital Damascus. (Amer Almohibany/AFP/Getty Images)

“We’re also seeing a huge increase in the number of civilian casualties. More and more people are being hurt because the intensity of bombing is greater,” he added. “It’s hard to imagine that the conditions in Syria could have become worse than they already were, but they have.”

Russia has in recent weeks escalated its attacks against areas of eastern Syria controlled by the Islamic State, but U.S. military officials, aid workers and Russia’s own military reports suggest that the majority of strikes are still being conducted against the northwestern rebel-held provinces of Latakia, Aleppo and Idlib that bore the brunt of the initial Russian onslaught in early October.

Those areas are controlled by an assortment of rebel groups ranging from moderates backed by the United States to al-Qaeda’s Syria affiliate, Jabhat al-Nusra, all of which are sustained at least in part by supplies from across the Turkish border.

They are also home to millions of people, including hundreds of thousands who have already been displaced by fighting elsewhere and many of whom are dependent on humanitarian aid to survive. The escalated fighting heralded by Russia’s intervention has newly displaced an estimated 260,000 people, according to a U.N. official in southern Turkey, who spoke on the condition of anonymity because he is not authorized to comment to the media.

Because Turkey is under pressure to stem the flow of refugees to Europe, it has severely restricted access to Syrians wishing to cross the border, leaving those afflicted by the fighting with no means of escape, said Nadim Houry of the advocacy group Human Rights Watch.

“People are basically running around from place to place looking for safety, but there’s nowhere for them to escape to,” he said. “It’s extremely bleak.”

Though it is impossible to confirm that civilians are being deliberately targeted, aid workers say the attacks on civilian infrastructure appear frequent and systematic enough to suggest that they are.

A grain silo that supplied wheat to Idlib province, 10 bakeries that collectively catered to at least 200,000 people and several mills and warehouses that stored flour are among the targets that have been hit since Nov. 24, according to the U.N. report. In an area of Aleppo province controlled by the Islamic State, a water treatment plant was bombed, and 1.4 million people are without water.

At a minimum, said McGrath, “there appears to be a repeated pattern of high-intensity bombing in areas where it’s unthinkable that you wouldn’t have an impact on civilians.”

A hub where truck drivers gather to collect supplies arriving from Turkey near the Bab al-Salameh border crossing was repeatedly struck three times in five days, halting not only aid supplies but also commercial deliveries of food, fuel and other necessities, the U.N. official said. And the warplane that destroyed a flour mill and bakery serving 50,000 people in the Idlib province town of Saraqeb on Nov. 27 hit nothing else on its bombing run.

“Of course it was deliberate,” he said. “This was very specific targeting.”

Among the medical facilities hit since the Russian intervention are 12 in northern Syria that are supported by Doctors Without Borders, said Pablo Marco, who is in charge of the agency’s programs in Syria and does not think the health centers were struck by accident.

“Of course it is impossible for us to have certainty, but the frequency with which bombs are falling in hospitals or very close to hospitals is enough to make it really seem that, yes, they are targeting hospitals,” he said.

The strategy of targeting civilian infrastructure is not new — the Syrian air force has also systematically targeted bakeries, hospitals and markets over the past four years of war. But the Russian intervention has added to the amount of available firepower, and Russia’s more-sophisticated warplanes can pinpoint targets more accurately, the U.N. official said.

The Russian intervention has so far produced only limited gains on the ground for forces loyal to Syrian President Bashar al-Assad, which have struggled to capitalize on the new advantage provided by Russia’s superior air capabilities.

Sowing chaos and hardship in areas that are loyal to the rebellion serves, however, to undermine and dismantle the support structures that sustain the fighters, most of whom come from the areas in which they fight and rely as much on the bakeries and medical facilities as their relatives in the civilian population, according to Aron Lund of the Carnegie Endowment.

The attacks cast doubt on the prospects for a peace process launched by world leaders at talks in Vienna last month, said Jan Egeland, secretary general of the Norwegian Refugee Council, one of the groups that has suspended its aid operations in northern Syria as a result of the attacks. He also warned of more misery ahead as winter descends.

“Civilians have been left with nowhere safe to flee. Schools, markets and bakeries are being bombed and women and children are under fire,” he said. “As humanitarian actors on the ground, we fear that intensified military intervention will once again undermine hopes for real peace talks.”

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