Al Qaeda leader Ayman al-Zawahiri has called for lone wolf attacks in the U.S. and the West.

In an audio message released Sunday, al-Zawahiri called on Muslims to "harm the countries of the crusader coalition."

"We must now focus on moving the war to the heart of the homes and cities of the crusader West and specifically America," he said.

Fox News chief intelligence correspondent Catherine Herridge reported on "Fox and Friends Weekend" that the 36-minute recording is being reviewed by U.S. intelligence analysts.

Herridge said that al-Zawahiri called for Muslim youths in the West look to the Tsarnaev and Kouachi brothers as examples to follow - the siblings who carried out the Boston Marathon bombings and Charlie Hebdo shootings in Paris, respectively.

She described it as "a standing order for terror," with no phone call, email or social media message to coordinate an attack.

"These operations are that much harder to disrupt, because there are no communications between them and the 'mothership' or the lead organization, in this case Al Qaeda in Yemen or Al Qaeda core in Pakistan," Herridge explained.

Watch more above.