The jihadists control a shrinking strip of land east of the Syria's Euphrates River around the town of Hajin, which U.S.-backed forces entered this month.
SDF commander-in-chief Mazloum Kobani told Reuters last week that at least 5,000 IS fighters remain holed up in the enclave, including many foreigners who appear ready to fight to the death.
Islamic State's self-proclaimed caliphate has crumbled after different offensives across Iraq and Syria, though its fighters still operate in the desert border region and mount attacks. (Reporting by Ellen Francis Editing by Andrew Heavens)
(With inputs from agencies.)