US President Barack Obama has insisted that his country's troops have no combat mission in Iraq.

His comments came after his top general suggested some US advisors could join Iraqi forces to fight the Islamic State group.

"The American forces that have been deployed to Iraq do not and will not have a combat mission," Mr Obama told troops at the headquarters of US Central Command in Florida.

Mr Obama has repeatedly stressed that, despite ordering air strikes against IS in Syria and Iraq, he will not send US troops back to fight another land war in the region.

Indeed, he has based much of the rationale of his presidency on getting US forces out of foreign entanglements.

But his remarks here were lent added relevance by comments yesterday by General Martin Dempsey, Chairman of the Joint Chiefs of Staff.

Gen Dempsey said that it may at some point prove necessary to send US advisors into action with the Iraqi troops battling IS, in what he called "close-combat advising".

But the White House insisted the idea of US troops in battle was a "purely hypothetical scenario".

It was not immediately clear whether Mr Obama's comments in Florida precluded such an approach, but there appeared to be plenty of rhetorical space for Gen Dempsey's scenario to play out while allowing Mr Obama to insist that US troops have no dedicated combat mission.

President Obama did not repeat the frequent US characterisation of the evolving mission in Iraq and Syria that there will be no US "boots on the ground" - a term usually seen to refer to combat troops.

Mr Obama's short remarks at the MacDill air force base also included a defence of his own foreign policy, which Republicans argue is collapsing around him.

He noted that he had brought US combat troops home from Iraq, refocused the US war in Afghanistan and would "responsibly" end combat operations in the country before the end of the year.

Mr Obama stressed that in the new conflict to "degrade" and "destroy" the US would not go it alone and talked up the international coalition he is building.

He said France and Britain were already flying with the US over Iraq and added that Australia and Canada would send military advisors to the country.

Mr Obama noted Saudi Arabia's willingness to base a US mission to train moderate Syrian rebels on its soil and said German paratroopers were also going to take part in a training mission that he did not specify.

Meanwhile, Iranian President Hassan Rouhani has denounced Islamic State's beheading of innocent people, saying the militant group wants to "kill humanity".

"From the viewpoint of the Islamic tenets and culture, killing an innocent person equals the killing of the whole humanity," Mr Rouhani told the US television network NBC.

"And therefore, the killing and beheading of innocent people in fact is a matter of shame for them and it's the matter of concern and sorrow for all the human and all the mankind."

IS has already killed US journalists James Foley and Steven Sotloff, and British aid worker David Haines. It is threatening to kill another British aid worker, Alan Henning.