Washington ( CNN ) The U.S. military is trying to gather as much intelligence as it can about ISIS defenses in Mosul to make a key decision about whether it 's necessary to recommend American ground troops accompany Iraqi forces on the looming fight to retake Iraq 's second largest city . The first move by Iraqi forces on the ground could come as soon as April , a U.S. Central Command official told CNN . ISIS is continuing to attempt to reinforce its defenses of Mosul . If those defenses grow to a significant level , then Iraqi forces may need U.S. help in locating military targets to hit , the official said . If ISIS defenses reach that critical point , the Pentagon and Central Command may then recommend to President Obama that U.S. troops be involved , the official said . Gen. Lloyd Austin , head of Central Command , and Gen. Martin Dempsey , chairman of the Joint Chiefs , have both suggested a small number of U.S. troops could be needed to help with targeting , but not to go into combat . Now there is a more specific explanation of the trigger — ISIS defenses — that could cause the recommendation to go to the President . The United States already is observing ISIS members protecting their families by sending them out of Mosul , the official said . Recent coalition airstrikes around Mosul have been aimed at cutting off all supply lines to ISIS in the city . That way , when the military operation begins , ISIS will be isolated inside Mosul and unable to reinforce its fighters . Centcom believes ISIS has lost the ability to gain significant new amounts of territory in Iraq and hold onto it , the official said . And in both Iraq and Syria , the assessment is that ISIS fighters are stretched so thin , leaders are having to make choices and prioritize where they want to put their resources and fighters , the official added . That became a key reason they abandoned the fight for Kobani . There is also some evidence that the number of foreign fighters coming into Syria and Iraq may have declined over the last four to five months . However , hostage killings videos do underscore that the ISIS social media propaganda campaign remains strong , the official said . U.S. military and intelligence officials are noting the highly produced nature of some of the videos indicate ISIS had spent considerable time on the efforts .
Iraqi forces could begin to move to retake Mosul as soon as April , a U.S. official says . The official, speaking on condition of anonymity because he was not authorized to discuss the matter publicly, said that if ISIS is pushed out in Mosul, it will be difficult for Baghdad and its allies to hold onto territory