BAGHDAD — The U.N.’s public health agency said today it has trained 90 Iraqi medics in “mass casualty management,” with a special focus on chemical attacks, as part of its preparations for Iraq’s operation to retake Mosul from the Islamic State group.

The extremist group, which has ruled Iraq’s second largest city for more than two years, is believed to have crude chemical weapons capabilities, and Iraqi forces say they are prepared to encounter them on the battlefield.

The World Health Organization said Wednesday that of the 700,000 people expected to flee Mosul, some 200,000 will require emergency health services, including more than 90,000 children needing vaccinations and 8,000 pregnant women.

The operation to retake Mosul began Oct. 17 and is expected to take weeks, if not months. The fighting has not yet reached the city itself, which is home to more than a million people.

Iraq’s special forces said today they have completed their objectives east of Mosul and are waiting on other forces to advance from the south to further isolate the city before moving in.

“The operation has not been stopped and is proceeding as planned,” Brig. Gen. Haider Fadhil said.

Iraqi forces have been battling IS militants around the town of Shura, some 25 miles south of Mosul, in recent days. Iraqi officials have said the offensive is proceeding according to plan and that some operations are ahead of schedule.

The Mosul offensive is the largest Iraqi military operation since the 2003 U.S.-led invasion, and involves more than 25,000 Iraqi soldiers, Federal Police, Kurdish forces, Sunni tribal fighters and state-sanctioned Shiite militias.

Fighting units are approaching the city from the north, east and south, and the U.S.-led coalition is carrying out airstrikes and providing ground support.

The International Organization for Migration says around 9,000 people have fled so far, but aid groups are preparing to receive 200,000 displaced people in the coming weeks and fear many more could flee before the operation is over.

The United Nations’ refugee agency is shipping tents, blankets and other aid from the United Arab Emirates to northern Iraq to help those affected by the military campaign.