OUTSIDE BAGHOUZ, Syria (AP) — U.S.-backed Syrian forces’ push to defeat the Islamic State group in its last, tiny bastion in Syria has been slowed by the presence of civilians and scores of prisoners held by the extremists, officials said Friday.The official with the Syrian Democratic Forces, who goes by his nom de guerre, Ciyager, said IS militants are still holding some 300 prisoners, both civilians and SDF fighters, adding that their fate is unknown.The military campaign to uproot the militants from the eastern banks of the Euphrates River began in September, pushing them down toward this last corner in the village of Baghouz, near the Iraqi border. The military operation has been halted several times since Feb. 12 as the SDF said a large number of civilians and hostages were holed up in the territory, a tent camp atop a network of caves and tunnels.This week, the SDF resumed its final push before reducing pressure due to strong resistance from the extremists and the surrender of hundreds of IS fighters and family members.Ciyager, the SDF official, said there are no negotiations underway to secure the prisoners’ release.An SDF statement said hundreds of IS fighters and their families surrendered Thursday. SDF spokesman Mustafa Bali tweeted that a new group of IS fighters surrendered Friday, without giving a number or further details.Another SDF official said an Islamic State suicide bomber approaching to surrender blew himself up at the checkpoint where they search evacuees. The official, who spoke on condition of anonymity because he was not authorized to discuss the incident, refused to say if there were casualties.The incident underscores how risky the operation is, and how it can be difficult for forces to tell civilians from combatants.Some fighters have surrendered in recent weeks, but hard-core militants, including many foreigners, are still holed up in the shrinking space along the eastern banks of the Euphrates River.SDF commanders have stopped speculating when the battle may finally be over. Already some 25,000 people have left Baghouz, thousands more than were originally believed inside. Commanders say they don’t know how many more may still be left, hiding in tunnels beneath the war-scarred village.On Friday the situation was quiet as aircraft flew over the area controlled by IS.The capture of the last pocket still held by IS fighters in Baghouz would mark the end of a devastating four-year global campaign to end the extremist group’s hold on territory in Syria and Iraq — a self-declared caliphate that at the height of the group’s power in 2014 sprawled across nearly a third of both countries.Also Friday, the Britain-based Syrian Observatory for Human Rights marked the eighth anniversary of the conflict by reporting that more than 570,000 people have been killed since March 15, 2011. The conflict began with pro-democracy protests and escalated into a civil war after a fierce government crackdown and the rise of an insurgency.Six million people have fled the country while a similar number are internally displaced.The Observatory said it has documented 371,222 deaths by name, including 112,623 civilians. The civilians include 21,065 children and teenagers as well as 13,173 women.The dead also include 67,000 rebels and army defectors as well as 115,000 government troops and pro-government fighters. Also killed during the conflict were some 66,000 militants, including al-Qaida-linked fighters and members of the Islamic State group.The Observatory estimates that 105,000 people died while in government jails, mostly under torture.