Iraqi forces said they launched new assaults in Mosul’s Old City on Monday after more than two weeks of only minor advances. Iraqi forces have discussed new tactics, which a United States military official said might include opening a second front and trying to isolate the Old City.

“Federal police and Rapid Response units started to advance in the southwestern part of the Old City” towards the al-Nuri mosque area, the police said in a statement on Monday. Reuters reporters on the ground saw helicopters carrying out strikes.

A March 17 explosion that killed between 60 and 240 people, according to conflicting accounts, cast a shadow over the United States-backed offensive to drive ISIS hardliners out of Iraq’s second largest city, and the parliament speaker spoke of ceasing operations until civilian casualties could be avoided.

The civilian death toll has increased in the more densely-populated west of Mosul as the militants have used homes for cover, drawing air strikes that have killed residents.

According to Reuters, Iraq’s federal police chief, Lieutenant General Raed Shakir Jawdat, said new advances, supported by air power, were being aided by “precise targeting of selected positions” provided by intelligence.

“Our advance aim is to protect civilian lives, infrastructure and private properties,” he was quoted by state TV as saying.

Another federal police officer said the attacks were “the start of the operations to seal off the Old City and prevent ISIS from receiving reinforcements and fleeing”. The objective, he said, was to “tighten the noose” around ISIS.