US President Donald Trump has ordered his generals to come up with an accelerated strategy to "eradicate" the group's so-called caliphate, and allied ministers are keen to hear more.
And it is also an occasion for Trump's discreet new secretary of state, Rex Tillerson, to emerge from the shadows and stamp his authority on the diplomatic side of the joint effort.
But eyebrows have been raised by Trump's plan to slash 28 percent from the State Department's budget for diplomacy and foreign aid, suggesting fewer resources for post-conflict stabilization.
European diplomats told AFP that they expect reassurances from Washington that it remains committed to a longer-term plan to secure the region after a battlefield victory.
The day-long ministerial-level discussion at the State Department will also help plan for the political aftermath of the battles for the cities of Mosul in Iraq and Raqqa in Syria.
Iraq's Prime Minister Haider al-Abadi was in Washington just ahead of the talks, and said victory against IS was within sight, if only the allies stick together.
"We are killing Daesh. We are proving that Daesh can be killed, can be eliminated," Abadi told an invited audience at the US Institute for Peace, using the group's Arabic acronym.
"We can do it not only in Iraq but in the region. I am encouraging our allies and our friends to stay focused. We shouldn't lose focus, we shouldn't give Daesh a second chance."
Shortly after taking office in late January, Trump gave the Pentagon 30 days to review progress in the anti-IS fight and develop a comprehensive plan to "totally obliterate" the group.
On the campaign trail, the combative candidate frequently bemoaned how long it was taking then president Barack Obama to get the job done - and he claimed to have a secret plan to finish IS.
But he never offered any details and so far has largely stuck with Obama's strategy.
This centres on US-led or guided forces carrying out continual surveillance and strikes on jihadist targets, while training and equipping local forces to conduct ground combat and hold seized terrain.
Still, Trump has made some notable tweaks, including granting commanders broader authority to make battlefield decisions.
Military officers had complained of micromanagement by the Obama White House, but critics worry the military may now lean toward actions with a greater likelihood of civilian deaths, such as a botched January raid in Yemen that ended up killing a Navy SEAL and multiple Yemeni women and children.
On Monday, the Pentagon confirmed that it was investigating allegations that a strike it launched on a suspected al-Qaeda target near a mosque in northern Syria killed dozens of civilians.
Last month, the Pentagon gave Trump an initial draft of its revised anti-IS plan.
Pentagon spokesman Navy Captain Jeff Davis said the document would "inform" Wednesday's diplomatic discussions, and that feedback from coalition partners would go back into the plan.
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