Mohammad Mohiedine Anis, 70, smokes his pipe as he sits in his destroyed bedroom listening to music on his vinyl player in Aleppo's formerly rebel-held al-Shaar neighborhood. (Joseph Eid/AFP/Getty Images)

Aid deliveries have all but stopped for hundreds of thousands of Syrians living under siege, a medical group said Tuesday, raising the risk of death from starvation, malnutrition or a lack of basic medical care.

As Syria’s war enters its seventh year, President Bashar al-Assad’s forces have recaptured all the country’s major urban centers while continuing to pressure what remains of once sizable rebel-held enclaves around the capital, Damascus, despite a nationwide cease-fire.

Caught in the crossfire are tens of thousands of civilians, most of them heavily dependent on United Nations aid deliveries that require approval of the Syrian government. 

Physicians for Human Rights (PHR), a New York-based group monitoring humanitarian conditions in Syria, said the flow of lifesaving humanitarian supplies has slowed to a trickle since the start of the year.

Only one U.N. convoy reached its destination in January, while two arrived in February, according to the group. 

Mohamed Ataya, a 31-year-old Syrian man known as "Abu Maher", tends to his plants on the rooftop of his damaged building in the Syrian rebel-held town of Arbin, in the eastern Ghouta region on the outskirts of the capital Damascus on March 3, 2017. Ataya, who used to be a professional football player before the war, cultivates seeds for sale. (Amer Almohibany/AFP/Getty Images)

Aid groups say that more than a million Syrians now live under siege without access to sustained humanitarian assistance. 

“Our findings show a clear pattern of obstruction and manipulation by Syrian authorities, who ensure that approved aid rarely reaches its intended targets, and when it does, it is wholly inadequate,” said Elise Baker, the organization’s lead Syria researcher. 

Humanitarian access was meant to accompany a cease-fire brokered in December by Russia and Turkey. But in January, Jan Egeland, a senior U.N. adviser, blamed the stoppage on a “complete, hopeless, bureaucratic quagmire.”

While the United Nations usually works at the invitation of the governments that host it, critics say the organization’s reliance on the approval of Assad’s security apparatus has allowed aid to be used as a weapon of war. 

In the besieged rebel-held town of Madaya, dozens of civilians starved to death last year after months without any aid deliveries. Although convoys have reached the area since then, doctors say their contents are often ill-suited to needs. Food deliveries have sometimes carried carbohydrates but no protein, leading to malnutrition among the area’s residents. Government soldiers have also removed antibiotics, anesthetics and burn treatment kits from trucks bound for areas where operating theaters had run dry, according to U.N. officials.

On Monday, a coalition of 81 relief groups, most of them Syrian, called for an end to the sieges, with full and unhindered humanitarian access and passage for civilians.

A man walks inside a damaged school in the rebel held besieged city of Douma, in the eastern Damascus suburb of Ghouta, Syria, on March 2. (Bassam Khabieh/Reuters)

Husam AlKatlaby, a representative of the Violations Documentation Center, a Syrian human rights group, said the Syrian army had cut off aid to an estimated 450,000 people in the Damascus suburb of eastern Ghouta, an area that attracted global attention in 2013 after a deadly chemical weapons attack by the Syrian government.

“Patients are already dying due to lack of medicine, food is becoming more expensive, and every day brings fresh casualties from conventional or chemical weapons. We fear that eastern Ghouta will be the next of many more Aleppos yet to come – cut off, strangled, and bombarded while the world watches,” said AlKatlaby, referring to the city retaken by Syrian forces at the end of last year after a punishing months-long siege and bombing campaign.

In a report released Monday, the U.N.’s Commission of Inquiry on Syria accused Assad’s army of launching a fresh round of chemical attacks on eastern Ghouta, this time involving chlorine. 

Fears are also growing for Syrian civilians trapped in the country’s northern provinces. One of the largest aid operations to Syria, run by U.S.-based Mercy Corps, was closed last week by Turkey, citing irregularities in the group’s paperwork. 

But humanitarian workers in the southern Turkish town of Gaziantep, speaking on the condition of anonymity because they were not authorized to brief journalists, said they feared the closure is part of a broader crackdown on aid groups operating there, and that it could affect hundreds of thousands of displaced and struggling Syrians across the border. 

“The situation could deteriorate very quickly,” said one aid worker. “These groups support bakeries, schools, and medical supplies. They support everything the people there are using to survive.”

Wednesday marks the sixth anniversary of the Syrian revolt, which began as a peaceful antigovernment uprising before turning into one of the deadliest armed conflicts of the 21st century. Almost a half-million people have been killed in the intervening years, while much of the country has emptied out. 

The U.N. children’s agency, UNICEF, said Monday that 2016 had been the worst on record for Syrian children, with more killed, maimed and recruited as child soldiers in a sharp escalation of violence. 

That fighting ebbed at the start of the year, after Turkey and Russia brokered a nationwide cease-fire between Syrian government forces and most of the rebel groups it is fighting. 

But the fighting has ticked steadily up once again as the Syrian army and allied Iran-backed forces press offensives against rebels around Damascus, the southern city of Daraa and the western city of Homs. 

Syria’s shaky cease-fire has been accompanied by several rounds of largely fruitless peace talks. The latest meeting was derailed Tuesday, after the rebel delegation said it would not be in attendance, citing the government’s continued airstrikes across the country.

The stuttering peace process has also caused the rebels to turn in on themselves. An alliance of al-Qaeda-linked militants opened attacks on armed groups that initially agreed to join the process. The U.N. Commission of Inquiry said Monday that the fighting had caused hundreds of casualties, with “serious repercussions” for the rebels’ ability to fight pro-government forces in future.