Baghdad — Iraqi forces said Saturday that they captured a key town about 9 miles south of Mosul, while an aid agency reported a sharp increase in the number of civilians fleeing since fighting reached the outskirts of the Islamic State-held city.

Government forces took control of the town of Hammam al-Alil after battling Islamic State fighters, Iraqi federal police chief Raed Chaker said.

Hammam al-Alil is the main town south of Mosul along the Tigris river, one of the lines along which Iraqi forces are advancing on the city.

Friday, government forces said they had captured six districts in eastern Mosul after entering the city’s boundaries three days earlier.

Prime Minister Haider Abadi, on what state television said was a visit to forward lines near Mosul, warned that a “fifth column” might engage in acts of terrorism “to aid Daesh (Islamic State) in the final moments.”

Abadi promised residents of the city that they would soon be liberated.

“My words to the terrorists are that if you wish to save your lives you should lay down your weapons,” he said. “There is no place for you in Iraq.”

Mosul is the only major Iraqi city still held by Islamic State.

Meanwhile, the Norwegian Refugee Council said Saturday that the number of displaced people had risen sharply, with over 9,000 new arrivals in camps the previous day.

“This is the beginning of a massive exodus from Mosul city,” Wolfgang Gressmann of the aid agency said. “We must insist that civilians fleeing have genuinely safe exit routes out of the city.”

The agency said at least 1.2 million people were thought to be trapped in Mosul and about 700,000 “might soon require humanitarian assistance.”