The Islamic State (formerly known as Isis) is already adapting to US-led air strikes in northern and eastern Syria by using the civilian population as human shields, according to a US military spokesman.
Lt. Gen. William C. Mayville noted that the Pentagon is unaware of any civilian casualties after a raid on Isis and other al-Qaida-linked groups and stressed that "limiting them is a top priority for the United States".
But he also warned that Isis is a "very adaptive and learning force" and said the US military has already seen evidence of jihadists mixing in the local population and using them as shields.
The practice of using civilian population as human shields is allegedly used by Hamas militant group in Gaza against Israeli strikes, according to the Israeli government.
During this year's offensive on the Palestinian territory, Israeli PM Benjamin Netanyahu accused Hamas of wanting to "pile up as many civilian dead as they can" to tarnish Israeli image on an international level.
"They use telegenically dead Palestinians for their cause. They want the more dead, the better," he controversially said.
Earlier, US president Barack Obama confirmed that American air forces hit a separate Islamist militant group, known as the Khorasan, along with Isis.
In his Pentagon address, Mayville noted that the group was planning an imminent attack against targets in Europe and the US as well as being involved in recruiting westerners.
"Intelligence reports indicated that the Khorasan Group was in the final stages of plans to execute major attacks against western targets, and potentially the US homeland," the US official said.