BAGHDAD, Jan 24 (Reuters) Iraqi forces have started preparing an offensive to capture the western side of Mosul from Islamic State, campaign commander Lieutenant General Abdul Ameer Rasheed Yarallah said. Popular Mobilisation "is preparing an operation in the next two, three days, to back up the operation to retake the right bank" of the city, on the western side of the Tigris river, Mosuliya TV cited him as saying on Tuesday. Popular Mobilisation is a coalition of predominantly Iranian-trained Shi'ite groups, formed in 2014 to take part in the war on Islamic State. It became officially part of the Iraqi armed forces last year. Iraqi officials on Monday announced that the eastern side of the northern Iraqi city has been taken from Islamic State, after nearly 100 days of fighting. REUTERS CJ PR1220