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 try to retake Baghdad as soon as possible , a U.S. official said . ISIS is continuing to try to reinforce its stronghold of Mosul .