Iraq’s military closed in on Wednesday on the center of Shirqat, a northern town in Salahuddin province, held by ISIS seen as a stepping stone in the campaign to recapture the terrorist group’s stronghold of Mosul.

The army, backed by local police and Salahuddin’s Tribal Mobilization forces, have taken 12 nearby villages since launching the operation on Tuesday morning, said Ali Dawdah, the mayor of Shirqat currently based in Erbil.

With air support from a U.S.-led coalition, the troops are now less than 3 km from the town center, according to Dawdah, who said he expected the campaign to be concluded within 48 hours.

Five security personnel and one civilian have been killed in the battle for Shirqat, where they face hazards including roadside bombs, mortars and snipers, said the mayor and a source in the Salahuddin Operations Command which oversees military operations in the area.

Shirqat lies on the Tigris river 100 km south of Mosul.

Tens of thousands of civilians are thought to be trapped in Shirqat and surrounding villages, which have been under ISIS control since the group seized a third of Iraqi territory in 2014.

Officials have warned for months of a humanitarian disaster inside, where residents living under the terrorist organizaton’s harsh rule say food supplies have dwindled and prices soared.

There has not been a large-scale displacement of civilians so far. Iraqi authorities hope the course of the battle will allow most residents to stay at home to avoid creating a humanitarian crisis as forces move towards Mosul.

Residents of Shukran and Houri villages told Reuters by phone they had begun waving white flags above their houses on Tuesday evening as the military advanced, but ISIS punished them with 50 lashes each.

Joint Operations Command spokesman Yahya Rasool told Agence France Presse on Tuesday that “the operation to liberate Shirqat started at 5:30 am (0230 GMT) from several directions… with the support of coalition forces.”

“We are making good progress,” he told AFP. ” Shirqat is important, we can’t move on Mosul and have terrorists control Shirqat.”

Prime Minister Haider al-Abadi, speaking from New York where he met U.S. President Barack Obama, said the same operation also included efforts to flush out ISIS militants from desert areas near Ramadi and Heet in the western province of Anbar.

U.S. and Iraqi officials have said the push on Mosul could begin in October, though there are concerns that not enough planning has been done for how to manage Mosul, Iraq’s second-largest city, if and when ISIS is kicked out.