Baghouz, Syria -- The die-hard ISIS militants still clinging to a tiny patch of ground in Syria appeared on Tuesday to be giving up the fight -- but the U.S.-backed forces who have been battling for two months to seize the sliver of land in the town of Baghouz haven't declared victory yet.

A video posted online by ISIS' propaganda wing on Tuesday showed the remaining fighters engaging the Syrian Democratic Forces (SDF) in firefights, but a militant narrating the end of the two-and-a-half-minute video appears to herald the end of ISIS' self-declared Muslim "caliphate" in Syria.

"The Crusaders and the apostates have thrown the Muslims out of their land, May Allah hasten his revenge," the man says. "We have done everything we could to defend Islam and our fellow Muslims… Oh Muslim brothers everywhere, we did everything we could, but there is no power but in God."

The SDF said on Tuesday that its forces had entered the ISIS camp in Baghouz, but they hadn't yet cleared it of militants.

CBS News correspondent Charlie D'Agata has been with the SDF fighters on the frontline of the final battle to retake Baghouz for weeks. He spent Monday night hunkered down against a dirt berm with the militiamen and women, as U.S.-led coalition aircraft flew overhead to continue hammering the remaining ISIS holdouts with missiles. Tuesday morning, the gun battles erupted again.

D'Agata said the SDF forces warned his team to keep their heads down -- just over the ridge was an ISIS position, and as soon as they arrived at the position they heard bullets whizzing overhead.

For weeks, American and coalition airstrikes have pummelled the tiny slice of land, not more than a few hundred yards wide. D'Agata said it was hard to imagine how anybody could survive the onslaught.

Yet by day the ISIS fighters emerge to fight the SDF -- some of whom look like teenagers -- again. Agri Kobani, one of the SDF troops, told CBS News they were taking aim at a group of ISIS fighters trying to hide behind trees.

He said there was progress against the terror group every day. But the progress has been incredibly slow -- hindered by the presence of far more human shields than had been anticipated, and by landmines.

The so-called caliphate has been reduced to little more than a junkyard heap of wrecked cars, but the hard-core ISIS holdouts have managed to defend it against everything America and its allies have been able to unleash -- for months.

D'Agata notes that he has been covering the "final fight against ISIS" since early January.

SDF commanders have stopped trying to guess how many ISIS fighters, or their families, remain in Baghouz -- or how long it's going to take to dislodge them.