Iran's president and foreign minister said on Wednesday that America could not defeat Islamic State (IS) militants using only airstrikes, even as US President Barack Obama stressed that he would not deploy military personnel in combat roles.

Iranian President Hassan Rouhani said bombing could play a part in beating IS, but that more troops and greater "sacrifice" would be required.

"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 in Tehran. "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 went on to condemn IS's brutality, saying that they wanted to "kill humanity". Iran has provided significant military assistance to Iraqi forces since IS overran a large swath of the north of the country in June.

The US has been conducting airstrikes on IS targets in Iraq since August, when the Sunni extremist group made a push into territory controlled by the Western-backed Kurdish Regional Government (KRG) and seemingly threatened the capital of Erbil. Obama said last week that he had authorized strikes in Syria too, although none have yet taken place.

Foreign Minister Mohammad Javad Zarif said on Wednesday that IS were a "menace" that must be dealt with. "This is not a threat against a single community, nor a threat against a single region... It is a global threat," he warned, speaking at an event held by Washington-based think tank the Council on Foreign Relations.

Zarif went on to say that US airstrikes would not be enough to beat the group. " It will not be eradicated through aerial bombardment, we need now to deal with these realities."

Instead he said that "most" participants of an anti-IS coalition announced in Paris this week were implicated in creating and supporting the group and called for that to stop. "A good number of US allies in the region have supported and armed it [IS]." he said, adding that other states had provided safe transit.

IS, he said, was "a frankenstein that came to haunt its creators" and the newly announced opposition group was a "coalition of repenters".

He also reiterated that he wished Iran had been included in the Paris talks. Neither it or Syria were invited.

Zarif did not directly accuse any coalition members of supporting IS, but both Qatar and Saudi Arabia have reportedly financed the group, while Turkey's porous borders with Syria have allowed thousands of foreign jihadis to join it.

Zarif was in the US to take part in talks on Iran's nuclear program, which began on Thursday.

Meanwhile, Obama reiterated that US military personnel would not play a combat role in Iraq. Speaking after being briefed by US Central Command in Tampa, Florida on Wednesday, Obama said that American forces would act in a support capacity only and operate as part of a coalition.

"The American forces that have been deployed to Iraq do not and will not have a combat mission. They will support Iraqi forces on the ground as they fight for their own country against these terrorists," he told troops at MacDill Air Force Base. "As your Commander-in-Chief, I will not commit you and the rest of our Armed Forces to fighting another ground war in Iraq."

The only successful long-term solution, he added would be to help US partners secure their own countries' futures. "We'll use our air power. We will train and equip our partners. We will advise them and we will assist them."

Obama's remarks came a day after his top military officer suggested that American boots on the ground might be required to defeat IS in Iraq. Speaking to a Senate panel, General Martin Dempsey, Chairman of the Joint Chiefs of Staff, said that while there were currently no plans to deploy US military advisors in combat roles, he could foreseeably recommend an expansion in their role during vital offensives such as an attempt to retake Iraq's second city of Mosul, which fell to IS in early June when the group overran a significant portion of the country's northern regions.

"It could very well be part of that particular mission - to provide close combat advising or accompanying for that mission," Dempsey said, according to Reuters, adding that Obama had told him to "come back to him on a case-by-case basis" to discuss military action.

White House Press Secretary Josh Earnest subsequently said that Obama had been clear that he "will not deploy ground troops in a combat role into Iraq or Syria," during a Tuesday press briefing.