WASHINGTON — An elite American Special Operations force has captured a significant Islamic State operative in Iraq and is expected to apprehend and interrogate a number of others in coming months, ushering in a new and potentially fraught phase in the fight against the extremist Sunni militant group.

American defense officials described the capture as a crucial development in battling the Islamic State but said it also raised questions about handling what is likely to be a growing group of detainees.

Although American commandos have captured a handful of Islamic State fighters in Iraq and Syria in discrete operations in recent years, the Pentagon is now faced with the prospect of detaining a larger group of captives and potentially reprising some of the darkest images of the war in Iraq, particularly the abuses at Abu Ghraib prison.

The American military has largely fought the Islamic State, also known as ISIS or ISIL, from the sky, and large numbers of Islamic State fighters have been killed in Iraq and Syria by American airstrikes. The 200-member Special Operations team, made up of many Delta Force commandos, arrived in Iraq in recent weeks and is the first major American combat force on the ground there since the United States pulled out of the country at the end of 2011.