A new report says more than one million Syrians are trapped in besieged areas, in a challenge to the United Nations, which estimates only half a million and has been criticised by aid groups for underplaying a crisis.
Peace talks to end the five year old conflict quickly fell apart last week in Geneva and are set to resume on February 25, while opposition negotiators insisted the Syrian regime lift sieges on civilians and Russian forces stop air strikes before talks could begin.
The new Siege Watch report, issued on Tuesday by the Netherlands-based aid group PAX and the Washington-based Syria Institute, comes a month after images posted online of emaciated children and adults led to an international outcry and rare convoys of aid being sent to a handful of Syrian communities.
The UN had not listed the town featured in the videos, Madaya, as a besieged town at the time. Skeletal people were seen in Madaya and parents gave their children sleeping pills to calm their hunger, aid workers who entered last month had reported.
According to the Siege Watch report, more than a million people are living in 46 besieged communities in Syria, more than double of what is listed by the UN. It says most of the besieged areas are in the capital, Damascus, and Homs. About 200,000 people are besieged in the eastern city of Deir Ezzor by both DAESH and the Syrian regime.
Electricity, running water, food, fuel and medical care are usually cut off and limited, the report says. Deaths have been reported from poisoning while scavenging for food, malnutrition, disease and hypothermia. Many communities are besieged for months while some have been besieged for years.
Estimates are based largely on information provided by local contacts in communities which include councils, medical workers and citizen journalists.
The UN raised its estimate last month by some 100,000, saying that 486,700 people are affected, which is still less than some aid groups and other estimates who argue that more urgency is needed in humanitarian response efforts.
"Many remain unaware of the extent of the crisis, and the international response has been muted as a result," the Siege Watch report says.
In meetings this week with UN officials and member states, PAX says it will call for the immediate lifting of sieges as a way to build confidence in the peace talks. Syria Institute executive director Valerie Szybala said the new report has not been shared with Syria's regime.
The UN says it considers an area besieged if three criteria are met: The area is surrounded by "armed actors," humanitarian aid cannot regularly enter, and civilians, including the sick and wounded, cannot enter and exit.
"Of course, differences of opinion do occur," Amanda Pitt, a UN humanitarian spokeswoman, said of criticism of the UN's estimates.
The aid group Doctors Without Borders goes well beyond the figure in the Siege Watch report, estimating that 1.9 million Syrians live in besieged areas.
Doctors Without Borders said it defines Syria's besieged areas as ones "that are surrounded by strategic barriers that prevent the regular and safe inflow of humanitarian assistance and the regular and safe outflow of civilians, the wounded and the sick."
The United Nations places an estimated 4.5 million Syrians into a separate category called "hard to reach," a step below besieged. It defines that as "an area that is not regularly accessible to humanitarian actors for the purpose of sustained humanitarian programming as a result of denial of access."
Doctors Without Borders said it doesn't use that distinction, "as the medical consequences for both types of region are similar." Medical supplies are almost never allowed in, it said, and medical evacuations are rarely allowed out.
The aid group has said that since convoys reached Madaya last month, at least 16 people there have died and at least 33 were in danger of dying of malnutrition.
The United Nations now considers the town of 20,000 as besieged.