"I do not count in the disease, but this means something, it has an impact on the enemy," he said.
The Pentagon has shown until now quiet on loss estimates inflicted on the Islamic State group (EI). A caution that dates including the Vietnam War, in which US officials regularly announced huge losses in their enemy - before losing the war.
Colonel John Dorrian the US Ari Force spokesman Combined Joint Task Force - Operation Inherent Resolve, in a briefing via video conference from Baghdad December 8, 2016, said his side the extent of losses in the EI in the battle of Mosul in Iraq.
"Hundreds of fighters have died," said he said. The IE sends to fight "young fighters, unfortunately, teenagers," he said.
The car bombs used by IE in Mosul do not have the same sophistication, he added. The jihadists now use "conventional vehicles" rather than armored vehicles that are much harder to stop.
"Their resources are beginning to run out," but the situation "remains extremely dangerous," said he said.
In general, the defense official welcomed on condition of anonymity, that the coalition had led "the perfect strike campaign ever conducted," because of the relatively small number of civilian victims from previous bombing campaigns.
The coalition has conducted nearly 16,600 strikes on Iraq and Syria since August 2014.
She admitted responsibility for the deaths of at least 173 civilians in both countries but is accused of underestimating the balance sheet. The Airways NGO based in London estimated that the bombs coalition killed actually more than 1,900 civilians.
The US official confirmed that the coalition has relaxed its rules there are about one and a half regarding the number of civilian casualties which may possibly be accepted if the military objective justifies.