UPDATE 2-U.S.-backed Syrian force attacks Islamic State enclave

The U.S.-backed Syrian Democratic Forces (SDF) launched an assault on Sunday against the final Islamic State enclave in eastern Syria, aiming to wipe out the last vestige of its self-declared "caliphate" that once spanned a third of Iraq and Syria. While the Baghouz enclave represents the last shred of populated land held by the jihadists, the group is still widely seen as a big security threat with remote territory elsewhere and the continued capacity to launch guerrilla attacks.

The SDF, spearheaded by the Kurdish YPG militia, has been poised to advance into the enclave for weeks, but has repeatedly held back to allow for the evacuation of civilians, many of them wives and children of Islamic State fighters. Mustafa Bali, head of the SDF media office, said no further civilians had emerged from the enclave at the Iraqi border since Saturday and the SDF had not observed any more civilians in the area, prompting the decision to attack.

"The military operations have started. Our forces are now clashing with the terrorists and the attack started," he said. Tens of thousands of people have streamed out of the shrinking territory held by Islamic State over the last months.

Bali said more than 4,000 militants had surrendered to the SDF in the past month. Earlier on Sunday, a Reuters correspondent saw SDF forces advance into a tented area of Baghouz after Islamic State fighters withdrew from it. SDF fighters gathered some ammunition and rifles left behind by the jihadists. (Reporting by Rodi Said in Deir al-Zor; Writing by Lisa Barrington; Editing by Kevin Liffey/Tom Perry)