Earlier US estimates had put the total population of IS fighters in Mosul itself at between 3,500 and 5,000. Photograph: (AFP)
The US military said IS militants are fleeing the city as the Iraqi-led offensive is slowly gaining territory
Islamic State group fighters are trickling out of Iraq's Mosul as the militants suffered heavy casualties, the general overseeing American military operations in the region told AFP on Thursday.
Army general Joseph Votel, head of the US military's central command, said groups of half a dozen or fewer IS fighters have been seen slipping out of the city as US-backed Iraqi and Kurdish peshmerga forces close in.
Some of them dump weapons and try to look like civilians, making it hard for coalition drones and planes to track them, Votel said, but some presumably are headed toward Raqa, the IS group's Syria stronghold.
"They don't have uniforms, so it is a little bit of a challenge. These aren't big groups, they aren't moving in military formations," the four-star general said, speaking from an undisclosed military base in southwest Asia.
"There are some that will get away, and I think that happens in a lot of cases. Nothing is 100 per cent, but in this case we are doing a pretty good job."
Between 800 and 900 militants have been killed in and around Mosul since the Iraqi-led operation to recapture the city began 10 days ago, he added.
Earlier US estimates had put the total population of IS fighters in Mosul itself at between 3,500 and 5,000.
Up to another 2,000 were thought to be in the broader region.
The offensive is seeing tens of thousands of Iraqi fighters advancing on Mosul from the south, east and north in a bid to retake the last major Iraqi city under IS control.
Iraqi and Kurdish peshmerga forces are pushing along several axes and have made relatively quick progress as they approach the city.
Some strategists question the Iraqis' decision to leave part of the city open, but Votel said there were advantages to doing so.
"It certainly provides a way for the refugees of the population to get out of there," the general said, and "it does provide an opportunity to limit destruction in the city itself".
Votel said he had spoken with Iraqi military leaders late Tuesday who told him that, as of that time, 57 Iraqi security forces had been killed and about 255 wounded.
For the Kurdish peshmerga, numbers were lower, with about 30 killed and between 70 and 100 wounded.
The US-led coalition backing Iraqi forces is also trying to defeat the group in Syria, where they retain parts of the north and the key city of Raqa.