The chief spokesman for the self-named "Islamic State" (IS), also known as Isis, has given the clearest indication yet that his fighters would actually welcome a ground war in Iraq and Syria against US troops.
In a 42-minute audio message uploaded to the internet the group's Syrian-born spokesman, who has taken the adopted name of Shaykh Abu Muhammad al-Adnani, mocks recent US air strikes and the moves to build an international coalition against Islamic State.
Addressing President Obama, the spokesman says: "Is this all you are capable of doing in this campaign of yours? Are America and all its allies... unable to come down to the ground?"
No military response?
Two things emerge clearly from the various references to the US-led campaign to confront IS in the Middle East.
The US and French air strikes in Iraq are causing IS real damage - it has no effective military response to them - and for a number of reasons it really wants the US to commit ground troops to the battlefield.
"They are aching for a conflict with the West," commented Dr Peter Neuman, Director of the International Centre for the Study of Radicalisation, in London.
"The execution videos [of Western hostages] were bait to provoke an over-reaction. As soon as there are Western boots on the ground it then becomes the old narrative of the West versus Islam and they can claim they are fighting the occupation. They are trying to suck us in."
After a lightning advance across northern and western Iraq in June, IS took control of town after town, capturing Iraq's second city of Mosul, the strategic Mosul Dam and threatening to overrun the Kurdish capital of Irbil.
But since then, US air strikes in support of Iraqi and Kurdish ground troops have halted the IS advance in many places and driven their forces off the Mosul Dam and out of several towns.
Last week the French air force joined in, launching from a base in the UAE. Australia is sending a squadron of Super Hornet attack jets, while Britain is still debating whether to expand its air operations from reconnaissance and humanitarian aid to an active combat role.
A number of countries, including Britain, have been supplying arms and ammunition to the forces confronting IS.
But IS's spokesman poured scorn on this in his speech, reminding the US that it had already captured much of the modern American weaponry supplied to Iraq's army which fled before their advance.
"Send arms and equipment to your agents and dogs... send them very much, for it will end up as war booty in our hands. Look at your armoured vehicles, machinery, weapons and equipment. It is in our hands. Allah granted it to us. We fight you with it."
Since the weak and demoralised Iraqi army is considered incapable of taking on IS itself, there has been speculation that US combat troops may have to return to Iraq to help it, having withdrawn in 2011.
President Obama, David Cameron and other Western leaders have publicly asserted there will be no "boots on the ground", although close to 1,000 US military personnel are already in Iraq.
A number of military and political commentators, including the former British Prime Minister Tony Blair, have said it will be impossible to eradicate IS without a ground offensive.
The IS spokesman seemed certain of it, saying: "You will pay the price when your sons are sent to wage war against us and they return to you as disabled amputees, or inside coffins, or mentally ill."
For Islamic State, the prospective benefits of Western troops engaging them on the ground are obvious.
They would at last have a chance to fight soldiers at close quarters, with all the propaganda impact that would have on people in the West.
But above all, it would turn a regional conflict that is predominantly pitting Muslim against Muslim into a global jihad against "Crusaders", which could see IS's recruitment soar exponentially.