Barack Obama will steel Americans for a prolonged battle against the Islamic State, despite devoting much of his presidency to avoiding sapping new entanglements in the Middle East.
Obama will summon the symbolic weight of a televised address to the nation at 9pm on Wednesday (11am AEST Thursday).
His hand forced by the radical group's sudden rise in Syria and Iraq, Obama will use a prime time address to argue that targeted military might and an international coalition can defeat IS, before it poses a threat to the US homeland.
But mindful of avoiding what he believes are the mistakes of the last decade, Obama will assure millions of television viewers that he will not send conventional ground troops back to Iraq to fight a group that has beheaded two US journalists.
It remains unclear whether Obama would also use the address on the ceremonial state floor of the White House - where he announced the success of a US operation to kill Osama bin Laden - to signal an expansion of US airstrikes against IS from Iraq into Syria.
But the New York Times and the Washington Post said late on Tuesday that Obama is in fact prepared to authorise air strikes in Syria. The Times quoted a senior administration official, while the Post cited foreign policy experts who have spoken to Obama in recent days.
The speech will also lack a definitive timeline for US operations against IS, after several reports cited senior officials as saying they could outlast Obama's presidency, which ends in January 2017.
"I think the American people need to expect that this is something that will require a sustained commitment," said White House spokesman Josh Earnest.
The address will come at a poignant time - on the eve of the 13th anniversary of the September 11 attacks, when Islamic radicalism on a mass scale scorched the US homeland for the first time, and drew America into exhausting overseas wars and a still unending anti-terror campaign.
Earnest said Obama would "talk about the risks that the United States faces, and he'll talk about the strategy that he has put together to confront those risks, to mitigate them, and ultimately to degrade and destroy ISIL," he said, using an alternative acronym for IS.
A White House official said Obama told congressional leaders on Tuesday that he did not need fresh permission for military action he is planning to take against IS, a question that has divided senior lawmakers.
The speech will represent a chance for Obama to redress criticism that he has been slow to respond to IS, amid fears fighters armed with Western passports could hit US targets.
The president started the work of creating an international coalition to take on IS at the NATO summit last week.
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