America's top military leader has told Congress that US ground forces could be deployed once more in Iraq.
Army General Martin Dempsey, the chairman of the Joint Chiefs of Staff, told a Senate panel that he would make the recommendation if the current US campaign to defeat Islamic State (IS) militants fails.
"To be clear, if we reach the point where I believe our advisers should accompany Iraqi troops on attacks against specific ISIL targets, I will recommend that to the president," said Gen Dempsey, using another name for the terrorist group.
Pressed to expand, he said he "would go back to the president and make a recommendation that may include the use of ground forces".
Tuesday's Senate hearing was disrupted by anti-war protestersPresident Barack Obama has previously said there will no combat role for American forces in Iraq.
Gen Dempsey spoke after American warplanes stepped up the offensive against IS targets in Iraq, pounding targets southwest of Baghdad in two raids on Sunday and Monday.
US personnel in Iraq are currently said to be serving purely in a combat advisory role to help Iraqi troops tackle the IS forces.
Gen Dempsey said that if Iraqi forces launched a major offensive to recapture Mosul, he might want US troops to accompany the Iraqi troops or provide close combat advice.
Aid volunteer Alan Henning (centre right) pictured before he left for SyriaHe also told senators the US was ready to strike the extremists in Syria.
"This will not look like 'shock and awe' because that is not how ISIL is organised," he said, "but it will be persistent and sustainable."
Gen Dempsey appeared alongside Defence Secretary Chuck Hagel, who warned the war would not be easy or brief.
"Victory is when we complete the mission of degrading, destroying and defeating ISIL," the Pentagon chief testified.
The Senate hearing was repeatedly disrupted by anti-war protesters.
British hostage David Haines was beheaded by his captorsBritish Foreign Secretary Philip Hammond said the UK Government was doing all it could to save British hostage Alan Henning, and warned it would not be deterred from its goal of "crushing" the Islamic State fighters behind his abduction.
Mr Henning, an aid convoy volunteer, appeared at the end of an IS video released on Saturday in which fellow UK hostage David Haines was killed, with a threat that he would be next.
Speaking to Sky News, Mr Hammond said he understood Mr Henning's family were "going through hell", and that the Government was doing everything possible to protect him.
An Islamic State gunman in Raqqa, SyriaBut he said the SAS, the elite British regiment, had not been sent in to rescue Mr Henning because it was not clear exactly where he was being held.
Mr Hammond was speaking after a summit in Paris where world leaders agreed to provide military aid to fight the extremist network.
The meeting of 30 countries agreed to "support the Iraqi government by any means necessary - including military assistance".
US Secretary of State John Kerry has been urging allies - especially Middle East and Gulf states - to show a united front, and one American official said several Arab countries had offered to join the airstrikes.