The UN food aid agency said Friday that it feared a rise in malnutrition among children trapped in besieged communities in Syria where fighting has halted supply convoys.
"The World Food Programme is concerned about the fate of many Syrians trapped in conflict areas and still in need of urgent food assistance," spokeswoman Elisabeth Byrs told reporters in Geneva.
"We are monitoring worrying reports emerging of malnutrition among children in besieged areas," she said.
The WFP works with Syria's Red Crescent to distribute aid supplies, but teams have been unable to reach 38 different locations since mid-2012, notably around the capital Damascus, Byrs said.
Among them is the town of Moadamiyet al-Sham, which has been under siege for months by the Syrian army.
"We've tried unsuccessfully nine times to reach Moadamiyet since last year," Byrs said.
Although some 3,000 people were evacuated last week, the same number or more are still thought to be trapped there, according to the UN.
"We are very concerned about the situation of those who remain," said Byrs.
Across Syria, there is little confirmed data about possible malnutrition levels, and UN agencies are trying to build up a clearer picture.
"We can only assume that the situation is getting worse by the day," said Byrs.
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There have been increasing reports that barring food aid has been deployed as a tactic by the Syrian regime to starve out areas held by rebel forces.
Byrs declined to comment on that claim, referring to general "insecurity".
But she cited government red tape and multiple checkpoints set up by different units on both sides in Syria's war.
"Of course it's the situation when you have ongoing fighting you cannot access. When you're prevented by armed forces from access, what can you do? You cannot risk the lives of their volunteers from the Syrian Arab Red Crescent or their colleagues," said Byrs.
An estimated 115,000 people have been killed in Syria and millions driven from their homes since a brutal crackdown on peaceful pro-democracy protests in March 2011 escalated into civil war.
The WFP provided food assistance to 2.7 million in September and a record 3.3 million last month, though it was still 700,000 short of its target.
"Each time there is an opportunity, we just deliver food. Sometimes it's possible, sometimes it's not possible," said Byrs.
Marixie Mercado, spokeswoman for the UN children's agency UNICEF, told reporters that in 2009, two years before the start of the war, just over nine percent of Syrian youngsters were classed as severely malnourished.
The impact of fighting has compounded the effects of five years of drought in parts of Syria.
"There is an upward trend in the number of children being treated with moderate and severe acute malnutrition. Most of these case are being reported from two referral hospitals in Damascus," Mercado told reporters.
"The current levels do not indicate a nutrition crisis. However, data is lacking from inaccessible areas where very limited information is available."