For one Kurdish neighborhood of Syria’s biggest city, Syria’s nationwide cessation of hostilities never seemed to kick in. Now the violence that has torn the neighborhood apart—including new accusations of chemical weapons use—is straining the country’s ceasefire.

Although it now looks increasingly shaky, the ceasefire brought a halt to much of Syria’s violence when it went into effect in February—except on the outskirts of Aleppo’s al-Sheikh Maqsoud neighborhood.

Syrian rebels say they’ve been repelling attempts by Kurdish forces inside the neighborhood to cut the last supply line to the rebel-held eastern half of Aleppo city. But residents of al-Sheikh Maqsoud say rebels have been shelling the neighborhood indiscriminately, killing more than a hundred civilians in the past two months, and now they allege rebels have shelled them with chemical gases. The human toll has outraged Kurdish forces elsewhere in the country and tested their commitment to the ceasefire, and the fighting has proved impervious to attempts at mediation by the ceasefire’s international sponsors.

“Our children are under the rubble, civilians are under the rubble!” said Muhammad Hajji, Aleppo city head of the Kurdish Democratic Union Party (PYD), speaking to The Daily Beast from inside al-Sheikh Maqsoud.

Syrians on both sides of the al-Sheikh Maqsoud fighting have been left fatally exposed by the front lines that were frozen in place at the start of the ceasefire.

There is only one precarious supply route into rebel-held eastern Aleppo, the Castello Road. The Syrian regime holds territory on both sides of the Castello, and if the road is cut, rebel Aleppo will be entirely encircled. Starvation has been weaponized elsewhere in the Syrian war, but the siege of half of Syria’s largest city could be a humanitarian disaster on a scale unprecedented in the conflict.

The al-Sheikh Maqsoud neighborhood sits just south of a key choke point on the road. Rebels say the Kurdish People’s Protection Units (YPG) and some local allies moved on the Castello Road in February as the regime’s forces and the YPG made a grab for other rebel areas north of the city. Since then, according to rebels, YPG snipers have targeted civilians on the road.

The YPG is the armed wing of the PYD, the Syrian affiliate of the Kurdistan Workers Party (PKK).

“The PYD’s forces started by cutting off the Castello Road with machine gun fire and shelling, and the regime helped with bombing and artillery fire,” said Haitham Abu Hammou, spokesman for Aleppo rebel faction al-Jabhah al-Shamiyyah. “We had to confront the danger of [the PYD] and stave off the specter of siege for hundreds of thousands of civilians in liberated Aleppo city.”

Al-Sheikh Maqsoud residents and Kurdish officials say the YPG has been defending the neighborhood against rebel attacks and that rebels’ warnings of a siege are just a pretense.

“The YPG have no intention, and have never had any intention, of targeting the Castello Road,” YPG spokesman Redur Xelil told The Daily Beast. “These factions use this propaganda as a justification to shell al-Sheikh Maqsoud.”

Al-Sheikh Maqsoud’s residents are in an impossible position, with the regime to the neighborhood’s south and hostile rebels to the north. Previously, the neighborhood had been loosely integrated politically into rebel-held eastern Aleppo. Now that rebel-YPG relations have imploded, the neighborhood is surrounded by hostile territory.

International mediators, including from the United States and the United Nations, have been unable to halt the fighting. Both warring sides have committed to the nationwide cessation of hostilities, and both claim to be acting in self-defense.

“We’ve tried to get [all the sides in al-Sheikh Maqsoud] to de-escalate, and we’re going to continue to try to deescalate,” said a Western official who agreed to speak to The Daily Beast on condition of anonymity. “But [the neighborhood] has this weird sense of somehow running on its own dynamic, slightly separate from the rest of the conflict.”

“We’ll abide by any agreement, so long as [the YPG] doesn’t target the road to Aleppo or [rebel-held] villages in the northern countryside,” said Col. Ahmed Uthman, military commander of Aleppo-area rebel faction Firqat al-Sultan Mourad. “And we emphasized that to the countries mediating.”

While the YPG and one smaller ally are defending al-Sheikh Maqsoud, the rebels on the other side apparently include more than a dozen factions, all with variant demands and negotiating positions.

Now Kurdish officials claim that rebels have shelled al-Sheikh Maqsoud with chemical weapons. On April 7, activists inside the neighborhood released video of four victims of the alleged attacks being treated with respirators. In a statement, a local administrator in the Kurdish Red Crescent described symptoms among the victims including shortness of breath and nausea that he said seemed to be the result of “internationally prohibited gases,” perhaps chlorine.

The Kurdish Red Crescent is not affiliated with the International Red Cross and Red Crescent movement. Due to the hostilities around al-Sheikh Maqsoud, outside relief organizations cannot reach the neighborhood.

Dan Kaszeta, a former U.S. Army Chemical Corps officer with 25 years of experience in chemical defense issues, told The Daily Beast that it was impossible to assess the allegations of chemical weapons use based on the videos posted from al-Sheikh Maqsoud. “Unfortunately, none of these [videos] are conclusive,” he said.

“Phosgene and Mustard [gas] are pretty well ruled out because they take many hours after exposure,” Kaszeta continued. “There’s no reason why chlorine couldn’t be the culprit. However, there are very few ways, by video analysis, to tell the difference between chlorine exposure and any of hundreds or thousands of other respiratory irritants, including normal smoke and hexachloroethane smoke, which is used in military smoke grenades.”

The chemical weapons allegations have gained traction after an April 7 statement by rebel faction Jaysh al-Islam saying it had disciplined one of its local commanders for using “weapons not authorized for use in these types of confrontations.” Jaysh al-Islam later clarified that it was referring to “modified Grad rockets,” not chemical weapons. The chemical weapons allegations and the mistaken claim that Jaysh al-Islam admitted to their use have been circulated widely in Kurdish media and were repeated to The Daily Beast by PYD officials. Rebels have strongly and uniformly denied that they have chemical weapons or used them in the neighborhood.

A Russian Foreign Ministry spokesperson echoed the charges on April 12. “Now the Jaysh al-Islam group has used chlorine in Aleppo, and it seems they aren’t even hiding this,” she said.

The allegations of chemical weapons use have drawn attention from the rebel shelling of al-Sheikh Maqsoud, which itself seems to be a violation of international law.

“International law does not just prohibit targeting civilians,” Hadeel al-Shalchi, Syria researcher for Human Rights Watch, told The Daily Beast. “It prohibits indiscriminate attacks, those that do not or cannot distinguish between military targets and civilians.”

“This can be when attacks are not directed at a military objective or when the weapons or their particular use are inherently indiscriminate, as in many cases of shelling of populated areas,” she told The Daily Beast. In an April 12 release, Human Rights Watch condemned what it called “likely indiscriminate attacks” on al-Sheikh Maqsoud.

Rebels who spoke to The Daily Beast strongly denied that they were indiscriminately bombing al-Sheikh Maqsoud. They argued instead that they were targeting YPG frontline positions in response to YPG attacks on civilians transiting the Castello Road.

“We reject any targeting of civilians, under any pretense,” said Haitham Abu Hammou. “These wartime ethics are among the most important things that distinguish us from the Syrian regime.”

Rebels have alleged that the YPG is using civilians as “human shields.”

“Legally, the offensive party is obligated to discriminate [between military targets and civilians], use proportionate force, and take precautionary measures when attacking,” said Osama Abu Zeid, a legal adviser to rebel factions. “The defensive party is obliged to distance himself from civilian areas and not set up military bases or rocket platforms near civilians, which the YPG hasn’t abided by.”

But al-Sheikh Maqsoud residents have posted videos of the chaotic aftermath of shelling on residential streets, and rebels have been filmed—before and after the beginning of the ceasefire—shelling al-Sheikh Maqsoud with locally manufactured weapons that are impossible to reliably aim. These include improvised “Hell cannons” that fire explosives-packed propane tanks, a weapon that has been employed previously against residential areas of regime-held west Aleppo.

“There’s nothing [hitting] the front lines! All the shelling is hitting the middle of al-Sheikh Maqsoud, hitting the civilians,” said PYD official Hajji.

Al-Sheikh Maqsoud’s residents have the bad luck of living in the smallest, most vulnerable pocket of PYD and YPG control. The Aleppo rebel factions now shelling in from the neighborhood’s edge say their motivations are local—defending the Castello Road—but many are undoubtedly still smarting after being routed by the YPG in the countryside north of the city earlier this year. Many also have close relations with Turkey, which is at war with its own Kurdish insurgency and seems intent on checking further Kurdish expansion inside Syria.

This political context, and the deepening enmity between rebels and Kurdish forces, mean a local settlement might be impossible.

Mezkin Ahmed, a political representative for the PYD’s Autonomous Administration government, argued to The Daily Beast that al-Sheikh Maqsoud’s fighting was an attempt by Turkey to sabotage the ceasefire. “Turkey won’t let the Syrian issue be solved in Geneva negotiations,” she said. “Because if it’s solved, then Turkey gets nothing out of it.”

“It’s impossible to deal with these armed factions with these old-fashioned, reactionary mentalities, who answer to the agendas of regional countries like Turkey, Saudi Arabia, and Qatar,” said PYD official Hajji, who also goes by the nickname “Abu Guevara.” (“Like Che Guevara—Bolivia,” he explained to The Daily Beast. “Since I was young, I was influenced by progressive thinking… and I was affected by the plight of oppressed peoples.”)

“We have no problem with the Kurds,” said rebel commander Col. Uthman. “Our problem is with these Kurdish parties [the PYD], which attack areas under opposition control.”

On April 9, rebels put forward an initiative to evacuate al-Sheikh Maqsoud’s civilians amid ongoing clashes. But rebels also said expelling the YPG from the neighborhood was “an urgent military necessity.”

There seems to be no clear endpoint to these battles between the YPG and Aleppo’s rebels, unless the cessation of hostilities definitively collapses, or the regime or its Russian ally lose patience and intervene to bomb the rebels. Al-Sheikh Maqsoud will only be spared by a dramatic shift in the lines of control in Aleppo city, a shift that could mean the siege and starvation of hundreds of thousands of residents in the eastern half of the city.

The continuation of Syria’s ceasefire—and the February front lines it locked in place—means at least a partial reduction in violence and bombing across the country. But in al-Sheikh Maqsoud, it means a neighborhood-sized war that civilians can’t escape.