More than one million Syrians are living under siege after nearly five years of war, a new NGO report said Tuesday, warning that the crisis was "far worse" than UN officials have acknowleged.

"New data gathered by Siege Watch shows that there are well over 1,000,000 Syrians under siege in locations in Damascus, Rural Damascus, Homs, Deir Ezzor and Idlib governorates," said the report jointly released by a Dutch group and a US-based institute.