By Yeganeh Torbati

WASHINGTON (Reuters) -- A U.S.-backed military operation that freed 70 hostages who had been held by Islamic State in Iraq produced a cache of intelligence, and U.S. forces supporting Iraqi troops are likely to undertake more raids in the future, U.S. Defense Secretary Ash Carter said on Friday.

Carter said he decided on the rescue mission after intelligence showed that executions were imminent and mass graves had been dug.

"When we find opportunities to do things that will effectively prosecute the campaign we're going to do that ... raids is one of those categories and I suspect that we'll have further opportunities in the future and we're going to avail ourselves of them," Carter said.

The U.S.-led coalition against the Islamic State will also intensify its assault on the group's oil production and sales enterprise, Carter said, pointing as an example to a recent strike against a pump station and site for crude oil production in eastern Syria.

Overseeing those efforts will be Lt. Gen. Sean MacFarland, who Carter placed in charge of counter-Islamic State activities in Iraq and Syria. Three general had previously shared responsibility.

MacFarland pioneered the use of a Sunni force called Sahwa (Awakening) that worked with U.S. troops to defeat al Qaeda in Iraq six years ago, Carter said.

"His efforts will be critical in the coming months as we continue to provide support for capable partners fighting on the front lines," Carter said.

(Additional reporting by David Alexander and Doina Chiacu; Editing by Sandra Maler andLisa Shumaker)