Daesh's ranks have been pared back by international and local military action in Iraq and Syria to their lowest level since Washington began monitoring the group, a senior official said Tuesday.
"Working by, with and through local partners, we have taken back 40 percent of the territory that Daesh controlled a year ago in Iraq and 10 percent in Syria," deputy Secretary of State Antony Blinken told US lawmakers in prepared testimony.
"In fact, we assess Daesh's numbers are the lowest they've been since we began monitoring their manpower in 2014," he added.
Blinken did not put a new figure on the size of the terrorist group's fighting force in his statement to the Senate committee overseeing funding for the State Department's program to counter terrorism.
But in September 2014, the last estimate to which Blinken referred, a US intelligence official told AFP that the CIA believed the group could put between 20,000 and 31,500 fighters in the field, both foreign fighters and local recruits.
Since then, US-backed Iraqi and Kurdish forces have pushed Daesh fighters back from the cities of Tikrit and Ramadi and taken territory in northern Syria.