An unprecedented joint statement from Al-Qaeda in the Arabian Peninsula and Al-Qaeda in the Islamic Maghreb urged their "brothers" in Iraq and Syria to "stop killing each other and unite against the American campaign and its evil coalition that threatens us all."
AQAP and AQIM also called on the people of 10 Arab countries that have joined the coalition against the Islamic State group to prevent their governments from acting against IS.
And it promised "dark days" to the "alliance of infidelity and evil".
But the joint statement, released on two jihadist Twitter accounts, called for differences to be set aside in the face of the growing coalition.
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"Make the unity of the infidel nations against you a reason for your unity against them," it said, accusing Washington of "leading a Crusader campaign against Islam and all Muslims."
"Stop the infighting between you and stand as one against America's campaign," it added.
"We call upon our people in... All the nations of this Satanic alliance... To stand before the face of their agent governments and prevent them -- by all legitimate means -- from going to war against Islam under the excuse of fighting terrorism," the statement said.
The statement also addressed those fighting to continue efforts to overthrow Syrian President Bashar al-Assad, warning them to "beware of being tricked by America... And thus being diverted from your path" and becoming its "pawns".