US military troops are intensifying pressure on Islamic State militants in Syria and Iraq, supporting local forces with an expanded air campaign and occasional direct action on the ground, US Defense Secretary Ashton Carter told lawmakers on Tuesday. At a meeting of the Senate Armed Services Committee, Carter told the lawmakers US forces aimed to intensify pressure on the Islamic State stronghold of Raqqa in Syria and the Iraqi city of Ramadi.Carter said he expected the coalition air campaign to intensify, with more aircraft and a higher tempo of operations. He also said the United States also wouldn't hesitate to support local forces with "direct action.""We won't hold back from supporting capable partners in opportunistic attacks against ISIL or conducting such missions directly whether by strikes from the air or direct action on the ground," he said.The top US military officer, Marine Corp Gen. Joseph Dunford, told the committee he would consider recommending putting US forces with Iraqi troops on the ground to fight against the Islamic State if that would improve the chances of defeating the militants."If it had operational and strategic impact and we could reinforce success, that would be the basic framework for which I would make a recommendation for additional forces to be co-located with Iraqi units," said Dunford.Dunford, the chairman of the Joint Chiefs of Staff, outlined four reasons it might be useful to put US troops with Iraqi forces: increasing the coherence of the military campaign, ensuring logistics effectiveness, boosting intelligence awareness and improving combined arms delivery.US President Barack Obama would have to approve any new plan for an increase in action on the ground in Iraq and Syria before troops could be deployed.