The United Nations said on Tuesday there were indications that poorer families in Mosul are struggling to feed themselves as a result of rising food prices amid disturbing claims that ISIS is killing civilians for refusing to cooperate with the jihadists in the northern Iraqi city.

“Key informants are telling us that poor families are struggling to put sufficient food on their tables,” U.N Humanitarian Coordinator in Iraq, Lise Grande, told Reuters. “This is very worrying.”

“In a worst case, we envision that families who are already in trouble in Mosul will find themselves in even more acute need.” Grande said. “The longer it takes to liberate Mosul, the harder conditions become for families.”

Six weeks after the launch of the offensive on Mosul, Iraqi forces moving from the east have captured about a quarter of the city, trying to advance to the Tigris river that runs through its center. A U.S.-led coalition is providing air and ground support to the operation that started on Oct. 17.

A U.N. human rights spokeswoman also said on Tuesday that ISIS militants have killed civilians who refuse to allow rockets and snipers to be sited in their houses or whom they suspect of leaking information or trying to flee.

“On Nov. 11, ISIS reportedly shot and killed 12 civilians in Bakir neighborhood of eastern Mosul city for allegedly refusing to let it install rockets on the rooftops of their houses,” Ravina Shamdasani told a regular U.N. briefing.

Information received by the U.N. also showed that militants publicly shot to death 27 civilians in Muhandiseen Park in northern Mosul on Nov. 25, and on Nov. 22 an ISIS sniper killed a seven-year-old running towards the Iraqi Security Forces in Adan neighborhood in eastern Mosul.