As aid agencies prepare to deliver food to Madaya, on the outskirts of Damascus and two other besieged towns in Idlib province, an estimated 400,000 people are living under siege in 15 areas across Syria, according to the UN.
A deal struck in recent days permits the delivery of food to Madaya, currently surrounded by forces loyal to Syrian President Bashar al-Assad, and the villages of Fouaa and Kefraya in Idlib, both of which are hemmed in by rebel fighters.
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Due to a siege imposed by the Syrian government and the Lebanese Hezbollah group, an estimated 42,000 people in Madaya have little to no access to food, resulting in the deaths of at least 23 people by starvation so far, according to the charity Doctors Without Borders (MSF).
Reports of widespread malnutrition have emerged, some of them suggesting that Madaya residents are resorting to eating grass and insects for survival.
In Kefraya and Fouaa, about 12,500 people are cut off from access to aid supplies by rebel groups, including al-Nusra Front.
On December 26, Syrian government forces set up a checkpoint and sealed off the final road to Moadamiyah, a rebel-controlled town on the outskirts of Damascus, demanding that opposition groups lay down their arms and surrender.
The Moadamiyah Media Office, run by pro-opposition activists, estimates that 45,000 civilians have been stuck in the area for more than two weeks.
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The organisation said on Saturday that a siege that started in April 2013 and lasted a year, resulted in the deaths of 16 local residents due to a lack of food and medicine.
It said the current conditions had killed one local resident so far this year: an eight-month-old boy who died from malnutrition on January 10.
Dani Qabbani, a Moadamiyah-based media activist, said the child died because of "the crippling siege being imposed by Assad's militias".
"They couldn't help him here in the only field hospital in the city," he told Al Jazeera. "Assad's checkpoints prevented his family from hospitalising him in Damascus.
"If the situation continues for another week, we are expecting a disaster for the 45,000 civilians [in Moadamiyah]."
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Describing the local population as worn down and scared, Qabbani said: "They don't want to go through what they did in 2013 again."
Sharif Nashashibi, a London-based analyst of Arab political affairs, says the government-imposed sieges in places such as Moadamiyah and Madaya have put rebel fighters under "double pressure".
"These sieges don't just wear down the fighters, they also causes them to see the population around them suffering and raises the concern that the population could turn against them," he told Al Jazeera.
"These sieges are war crimes. The government is collectively punishing the population of that area because of the presence of 'enemy' fighters."
The UN reported in December that the Syrian government and allied militias have also placed under siege more than 181,000 people in the Damascus outskirts, including Darayya and Ghouta, as well as in Zabadani, near the Lebanon border.
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Separately, the Islamic State of Iraq and the Levant (ISIL) group has imposed a siege on more than 200,000 in Deir Az-Zor in Syria's east.
"Besieging Syrian civilians is wrong, whoever the perpetrator," Nashashibi told Al Jazeera.
"One cannot be selective in one's outrage over the suffering of Syrian civilians and plausibly claim to have a moral compass."
The ongoing Syrian conflict started as a largely unarmed uprising against President Bashar al-Assad in March 2011, but morphed into a full-blown civil war that has killed more than 250,000 people and turned more than 4.3 million others into refugees, according to statistics by the UN.
Juliette Touma, a spokeswoman for the UN children's agency UNICEF, says that the lack of access has made it impossible to assess the humanitarian needs of the communities in question.
"These are areas that have been under siege by parties to the conflict," she told Al Jazeera.
"We can't point a finger to one party and not another because more than one party to the conflict is involved in besieging various communities."
In addition to struggling to get food and medicine, Touma said, the affected areas also endure severe disruptions in, if not a total lack of, other basic services, including electricity and education.
Furthermore, she said, communities classified as besieged are not the only ones in desperate need of humanitarian access.
"Due to raging battles and increasing violence, there are more than 4.5 million people living in areas classified by the UN as 'hard to reach'," Touma said, adding that more than half of those are children.
Follow Patrick Strickland on Twitter: @P_Strickland_
Source: Al Jazeera