Fierce fighting erupted in Mosul on Tuesday as Iraqi forces tried to drive Islamic State militants from one of their last bastions in the eastern half of the city, while aid groups expressed concern for the estimated 750,000 people still in the militant-held west.

Hundreds of civilians fled from the northeastern Rashidiya neighborhood on foot as Iraqi helicopters circled overhead and fired on militants. At least two wounded Iraqi soldiers were brought back from the front lines after a suicide bombing.

A mortar attack in another neighborhood in eastern Mosul killed an Iraqi army colonel on Sunday, according to Brig. Gen. Yahya Rasool, a military spokesman.

Iraqi forces have seized nearly all of Mosul east of the Tigris river, which runs through the heart of the northern city, since the U.S.-backed offensive began in October.

The U.N. Humanitarian Coordinator for Iraq, Lise Grande, expressed concern for civilians in the western half of the city in a statement signed by 20 international and local aid groups. She said the cost of food and basic goods is soaring, water and electricity are intermittent and that some residents are forced to burn furniture to keep warm.

“We hope that everything is done to protect the hundreds of thousands of people who are across the river in the west,” Grande said in the statement. “We know that they are at extreme risk and we fear for their lives.”

The statement called on warring parties “to uphold their obligations under international humanitarian law to protect civilians and ensure they have access to life-saving assistance.”

Mosul is the IS group’s last major urban bastion in Iraq. The extremists still control large areas in neighboring Syria.

In Geneva, a spokeswoman for the U.N. human rights office said it had received “reasonable corroboration” for a report that 19 civilians were killed in an airstrike in the al-Jadida neighborhood of IS-controlled western Mosul last week.

“Attributing responsibility for airstrikes is very difficult,” Ravina Shamdasani said, adding that “it is clear that civilians are being killed in airstrikes.”

A U.S.-led coalition and Iraq’s own air force have been carrying out airstrikes in support of the Mosul operation.

The U.N. human rights office also said IS fighters have taken over “many hospitals” in western Mosul and are using them as military bases. It said the extremist group is diverting food, water and medicine to its fighters.

In Baghdad, meanwhile, a car exploded inside a dealership in the eastern Nahda area. The Interior Ministry said a bomb had been planted on the vehicle and that the blast caused no casualties. A police official and a medical official, speaking on condition of anonymity because they were not authorized to speak to reporters, said the blast killed at least two people and wounded seven.

Story by The Associated Press