BEIRUT -- Mohammed Khous was walking from the field hospital heading for his son's house nearby to rest between operations. He would never make it: a sniper's bullet to the head felled the 70-year-old in the street. With that, the Syrian town of Zabadani -- under heavy siege by government forces and allied Hezbollah militia -- lost its last doctor.

His killing last month drew attention to the continuing severity of Syria's blockades, despite international efforts to defuse them as part of ongoing peace negotiations in Geneva.

Dozens of people have died in the past year from starvation or illness related to malnutrition in besieged areas across Syria. Nearly half a million Syrians are trapped in sieges, according to the United Nations, and humanitarian aid convoys have only been able to reach 30 per cent of them this year. Most are besieged by government forces and another 200,000 by the Islamic State group, the Secretary General's office told the U.N. Security Council on March 23.

"The daily misery in these areas shames us all," Stephen O'Brien, the U.N.'s Under Secretary General for Humanitarian Affairs, told the Security Council.

Conditions in Zabadani -- once a popular mountain resort -- are a microcosm of the cruel reality that has beset Syrians across the country.

Dr. Khous was known to Zabadani residents as a generous and skilful surgeon who would recite poetry at the town' s cultural centre before he was sucked into the country's spiraling civil war.

"He had a knack for verse," said Amer Burhan, the administrator of the town's field hospital. "He loved Zabadani. He would sing about it."

After security forces launched a brutal crackdown against anti-government protests in 2011 in the prelude to the country's bloodstained conflict, Dr. Khous began quietly treating wounded demonstrators in his clinic in the nearby town of Baqin. Security forces were tracking down medical personnel who treated demonstrators, and he could not afford to attract the attention of government informers.

In 2012, the Free Syrian Army, which is aligned with the protesters, expelled government forces from Zabadani.

When the last surgeon left the town in 2015, Dr. Khous moved there to staff the operating room. One employee of the Syrian American Medical Society (SAMS), which supports medical facilities in the country, said rebels forced Dr. Khous to fill the vacancy. The employee spoke on condition of anonymity, fearing repercussions.

It was there that Dr. Khous became trapped in one of the harshest sieges of the war, after Lebanon's Hezbollah militia alongside government forces waged a pitiless campaign to dislodge rebel militias from the town. The Hezbollah campaign sent almost all of the town's civilians fleeing to neighbouring Madaya, which also fell under siege to government and Hezbollah forces last year. Engineers mined the areas around the two towns, and snipers took up positions to prevent anyone from entering or leaving.

For a while, Dr. Khous worked with Dr. Amal Awad Tatari, who did not have surgical training. But in January, she agreed to leave as part of a deal brokered by the U.N. between government and opposition forces to release injured people from four besieged towns across Syria.

She didn't want to go, but she had sustained an injury a year earlier and the suffocating siege became too much for her to bear.

"It really exhausted us and my health deteriorated. I have a wound to my head, shrapnel in my hand and a slipped disk. It reached a point where I couldn't walk," she said from Turkey, where she is receiving treatment.

Tatari said the conditions inside the hospital were dire.

"We would have to ration the sterilization kits," she said. "You can't believe how difficult it was."

Dr. Khous remained collected and professional, but the siege was taking its toll.

"You could sense he was living in another world, sometimes. We would be in the hospital for example, and there is shelling, but there are no injuries, and he's sitting writing poetry," Tatari said.

"We want to rebuild you, a paradise / O', my heart, Zabadani," he wrote in one poem shared by the SAMS with The Associated Press.

Dr. Khous continued to treat the gunshot and shelling wounds that regularly afflicted the 500 or so remaining residents on his own. SAMS was debating whether to cut support to the hospital, because most of those remaining in Zabadani were fighters.

Then, on March 25, Dr. Khous was shot by a sniper on his way back from work.

"We received a phone call that there was a martyr and we went and found Dr. Khous on the road," said the hospital administrator, Burhan. "He was shot in the head -- it was aimed to kill."

The bullet came from the direction of the siege, said Burhan. "We are 95 per cent sure he was killed by a government or Hezbollah sniper," he said.

Tatari said two others in Zabadani were killed by snipers that day. She said there was no way Dr. Khous could have been confused for a militant. He never carried a weapon, she said, and he was always dressed as a civilian. "You could tell, too, that he was advanced in age. It was clear from a distance," she said.

It took rescue workers three hours to remove his body from the street as snipers forced them to take cover.

A few days later, another man was shot in Zabadani. Ibrahim Ahmad Deeb was a close friend of the hospital administrator, Burhan. "He suffered a pretty serious wound, and as we do not have doctors, we didn't know how to treat him," Burhan said. "We watched him pass away."