More than one million Syrians are trapped in besieged areas, a new report says in a challenge to the United Nations, which estimates just half that amount and has been accused by some aid groups of underplaying a crisis, the Associated Press reports.

The new Siege Watch report, issued Tuesday, February 9, 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 to a handful of Syrian communities.

The town featured in the images, Madaya, was not listed by the UN as a besieged community at the time. Aid workers who entered last month reported seeing skeletal people and parents who gave their children sleeping pills to calm their hunger, AP says.

The Siege Watch report says 1.09 million people are living in 46 besieged communities in Syria, far more than the 18 listed by the UN. It says most are besieged by the Syrian government in the suburbs of Damascus, the capital, and Homs.

In the eastern city of Deir el-Zour, about 200,000 people are besieged by both the Islamic State group and the Syrian government. The report lists two communities besieged by armed opposition groups.

The estimates are based largely on information provided by local contacts in the communities, including local councils, medical workers and citizen journalists.