U.S. troops are intensifying pressure on Islamic State militants in Syria and Iraq by supporting local forces with an expanded air campaign and occasional direct ground support, U.S. Defense Secretary Ash Carter told lawmakers on Tuesday.

Testifying alongside Carter before the Senate Armed Services Committee, Marine Corp Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said he would consider recommending putting U.S. forces with Iraqi troops to fight Islamic State if it improved the chances of defeating the militants.

Carter said the campaign against IS was evolving as the U.S. military sought to reinforce ground efforts. He said U.S. forces aimed to intensify pressure on IS strongholds in Raqqa in Syria and Ramadi in Iraq.

Carter expects coalition air campaign to intensify, with more aircraft and an increased tempo of operations. He said the United States wouldn't hesitate to support local forces with "strikes from the air or direct action on the ground."

Dunford said that putting U.S. troops with Iraqi forces could ensure logistics effectiveness and boost intelligence awareness.

A raid against IS last week in which U.S. forces advised Kurdish forces resulted in the death of an U.S. soldier and the rescue of around 70 hostages.

"If it had an operational or strategic impact and we could reinforce success, that would be the basic framework within which I'd make a recommendation for additional forces to be co-located with Iraqi units," Dunford said.

(Reporting by Yeganeh Torbati, Phil Stewart and David Alexander; Editing by Doina Chiacu and Jeffrey Benkoe)