Iranian President Hassan Rouhani on Wednesday criticized the United States for its refusal to send troops into combat in the battle against Islamic State militants he claimed were seeking to "kill humanity."

Speaking in an interview with NBC television in Tehran before heading to the United Nations ahead of next week's general assembly, the Iranian leader appeared to question whether the US could achieve victory over the IS group without putting boots on the ground.

"Are Americans afraid of giving casualties on the ground in Iraq? Are they afraid of their soldiers being killed in the fight they claim is against terrorism?" Rouhani told NBC according to excerpts of the interview.

"If they want to use planes and if they want to use unmanned planes so that nobody is injured from the Americans, is it really possible to fight terrorism without any hardship, without any sacrifice?

"Is it possible to reach a big goal without that? In all regional and international issues, the victorious one is the one who is ready to do sacrifice."

Rouhani said while airstrikes were necessary in "some conditions and some circumstances", they should only go ahead with the "permission of the people of that country and the government of that country."

US President Barack Obama has ruled out deploying US troops on the ground against the Islamic State group.

US warplanes began airstrikes against the brutal extremist organisation's fighters in Iraq last month while building an international coalition against the group.

While critical of the United States' reluctance to send troops into battle, Rouhani said the Islamic State group must be stopped.

The group's executions of American journalists James Foley and Steven Sotloff and Briton David Haines were at odds with Islamic tenets, he said.

"They want to kill humanity," Rouhani told NBC.

"And from the viewpoint of the Islamic tenets and culture, killing an innocent people equals the killing of the whole humanity.

"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."

Rouhani said Iran would provide Iraq with any support necessary but stressed a "red line" would be crossed if IS fighters moved on Baghdad or holy sites.

"We will not allow Baghdad to be occupied by the terrorists or the religious sites such as Karbala or Najaf be occupied by the terrorists," he said.