The US-backed Syrian Democratic Forces say the Islamic State group has lost its last bit of territory in Syria, bringing to an end its “caliphate”.
A spokesman for the SDF declared the “100% territorial defeat” of IS.
The jihadist group once controlled 88,000 sq km (34,000 sq miles) of land stretching across Syria and Iraq.
Despite the loss of territory, the group is still seen as a major security threat capable of mounting attacks in the region and worldwide.
The Kurdish-led SDF alliance began its final assault on IS at the start of March, with the remaining militants holed up in the village of Baghuz in eastern Syria.
The alliance was forced to slow its offensive after it emerged that a large number of civilians were also there, sheltering in buildings, tents and tunnels.
“Syrian Democratic Forces declare total elimination of so-called caliphate and 100% territorial defeat of Isis [the IS group],” Mr Bali, the head of the SDF media office, tweeted.
“On this unique day, we commemorate thousands of martyrs whose efforts made the victory possible.”
SDF fighters have been raising yellow flags in Baghuz to celebrate their victory.
But despite the fall of Baghuz, IS is by no means defeated. US officials believe IS may have 15,000 to 20,000 armed adherents active in the region, many of them in sleeper cells, and that it will return to its insurgent roots while attempting to rebuild.
Even as its defeat in Baghuz was imminent, IS released a defiant audio recording purportedly from its spokesman Abu Hassan al-Muhajir, asserting that the caliphate was not finished.