The Syrian government has been blocking food and medicine from entering and people from leaving besieged areas, in what one security official calls "starvation until submission campaign", according to a Reuters report.
Forces loyal to President Bashar al-Assad have used partial sieges to root out rebel forces from residential areas during the civil war. But a recent tightening of blockades around areas near the capital Damascus is causing starvation and death, residents and medical staff told the news agency.
Community groups step in to help Syrians under siege
Food and medicine, which could be used by the warring parties, are rarely allowed to enter besieged areas and the movement of civilians in and out is restricted, Reuters said on Wednesday.
The UN says that more than one million Syrians remain trapped in areas where aid deliveries have stalled.
The UN Office for the Coordination of Humanitarian Affairs said in a report last month that half of those people are in rural Damascus and about 310,000 people more trapped in Homs, a province in central Syria.
Reuters reported that at a checkpoint in central Damascus, a state security official, known as Abu Haidar, was heard to say: "We like to call it our Starvation Until Submission Campaign."
The Syrian government has not commented on accusations it is using hunger as a weapon of war. It says that residents have been taken "hostage by terrorists".
Aid workers say they are denied access. Both sides use checkpoints to mark territory and prevent the movement of enemy fighters and supporters.
Rebel-held towns to the east, south and west of Damascus are under partial or total siege, and Abu Haidar said that the army had begun to block off the towns of Qudsayya and Hameh, a 15-minute drive north from central Damascus onto the Qasioun mountain range.
'Smuggling of bread'
Residents of these two towns said that earlier this month, on the first day of the Muslim holiday of Eid al-Adha, many were forbidden from leaving to visit family elsewhere.
The main checkpoint forbids most cars from entering or leaving the two towns, forcing people to get out of their vehicles, walk down the highway for 20 minutes and use public transport on the other side.
Soldiers, according to Reuters, conduct vehicle and body searches to prevent "smuggling" of bread, baby milk and medicine into the besieged area and jailing offenders.
The checks create long queues of residents trying to return home, sometimes forcing them to wait for hours, the news agency says.
All traffic is prevented from entering Hameh, a mostly Sunni Muslim town where many residents support the rebellion.
There is some movement into Qudsayya, a more religiously mixed area that is home to tens of thousands of displaced Syrians from other parts of the country.
For months, international pressure has been mounting on Syrian authorities to open humanitarian corridors to deliver aid to the besieged civilians.
Under international law, siege is not specifically prohibited. However, deliberate starvation in a conflict is widely held to be a war crime and the law of armed conflict requires all sides to allow free access of humanitarian relief for civilians in need.
Although Syria is not party to the International Criminal Court - which can prosecute war crimes - the UN Security Council has the power to refer cases.