US Secretary of State John Kerry discussed the Islamic State threat with the head of the Arab League, ahead of the group's next round of discussions.
The Arab League is due to hold a ministerial meeting in Cairo on Sunday to address fast-moving changes in the region.
Kerry and Arab League chief Nabil al-Arabi "discussed the need for the Arab League and its members to take a strong position in the coalition that is developing against ISIL," a senior State Department official said, using one of the acronyms by which the Islamic State is known.
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They also spoke of "the importance of decisive action to stop the flow of foreign fighters, counter ISIL's financing and combat its incitement," the official added.
Both men agreed that Iraq is on the frontline in the struggle against IS "and that Iraq, the United States, the region, and the international community must stand together to assist Iraq in facing this threat," the official said.
Iraq earlier welcomed US President Barack Obama's plan for an international coalition against jihadists as a "strong message of support," after repeatedly calling for aid against the militants.
Obama outlined the plan at a NATO summit Friday for a broad coalition to defeat IS, which led an offensive that overran chunks of five Iraqi provinces in June and also holds significant territory in neighboring Syria.