Mosul Province, Iraq (CNN) -- Kurdish forces fired mortars and explosives at extremist militants Sunday as the battle to retake a strategic dam in northern Iraq raged on. Smoke rose from the horizon, buildings were ablaze and the sound of massive explosions filled the air near Mosul Dam. By Sunday evening, the Kurdish forces -- known as the Peshmerga -- had taken over the eastern side of the structure, a spokesman for the group said. Clashes were ongoing over the western side, Peshmerga spokesman Halgord Hikmat told CNN. The forces face a daunting challenge: fighting a fierce offensive to retake the dam without damaging it.
@highlight
Obama sends letter to Congress, stressing dam's strategic importance
@highlight
ISIS wants to keep Mosul Dam working, CNN analyst says
@highlight
Peshmerga spokesman: Forces have retaken one side of the dam
@highlight
Smoke rises from the horizon, and buildings are ablaze in the battle to retake it
Mosul Dam is under @placeholder control, but it is still up and running, the colonel said.