IS income drops 30 percent on lower oil, tax revenue: IHS

An Islamic State flag hangs amid electric wires over a street in Ain al-Hilweh Palestinian refugee camp, near the port-city of Sidon, southern Lebanon January 19, 2016. REUTERS/Ali Hashisho

BAGHDAD (Reuters) - Islamic State's income and the population under its control have both fallen by about a third, a U.S.-based analysis firm said, describing the declining revenue as a threat to its long-term rule over its self-proclaimed caliphate.

Revenue for the ultra-hardline Sunni Muslim group, also known as ISIS or ISIL, fell to $56 million (£39.53 million) a month in March from around $80 million a month in the middle of last year, the analysis company IHS said.