The summit on countering violent extremism on September 29 comes one year after Obama vowed to crush IS during his United Nations speech.
Since then, the jihadists have captured territory in Syria and Iraq and gained a foothold in Libya, Yemen and elsewhere in the Middle East, with alliances as far afield as Nigeria's Boko Haram.
On Wednesday, IS released a picture on Twitter of a Croatian hostage abducted in Egypt, who apparently was the latest victim of the group's horrific beheadings.
Diplomats said the summit, to be held on the sidelines of the annual UN General Assembly meeting, will allow leaders to take stock and chart a way forward in the campaign to defeat Islamic State.
Obama last year hosted a Security Council meeting during which a resolution was adopted to curb the flow of foreign fighters joining IS extremists on the battlefields in Iraq and Syria.
But UN monitors report that the number of foreign jihadists has grown to at least 22,000 and there is no sign that the flow is abating.