An Al-Qaeda front group based in Iraq and Syria called for Egyptians to take up arms against their country's military, in an audio message posted on the Internet on Saturday.
The Islamic State of Iraq and the Levant (ISIS) also dismissed the Muslim Brotherhood, the party of ousted Egyptian president Mohamed Morsi, as "evil" for supporting democracy and seeking to win power through elections.
Following massive popular protests against the Islamist Morsi, the army removed him in a July 3 coup and imprisoned him.
"Today, we are affirming that these armies are infidels... and there is an obligation to fight them, especially the Egyptian army," the group's spokesman Abu Mohammed al-Adnani purportedly said in the half-hour audio message.
"The Egyptian army is... working very hard to install secularism and rule by secular laws."
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"The Egyptian army is an army which protects usury, brothels, Jews, Copts and Christians, who are fighting Allah and his Prophet. It is an army that attacks mosques and the Koran and killed and wounded people in peaceful demonstrations."
"Is this an army that cannot be fought against?"
Adnani also derided the Muslim Brotherhood as a "secular party in disguise as Islamists."
"They are even more evil and worse than secularists. They are a party which worships positions, and parliament. They were fighting to the death for the sake of democracy, but they are not fighting for jihad in the name of Allah."
The recording could not be independently verified.
ISIS has focused its activities on Iraq but, since peaceful protests against President Bashar al-Assad in early-2011 turned violent, also in neighbouring Syria.
In Iraq, it is widely blamed for a surge in violence in recent months that has left more than 3,800 people dead. And in Syria, it is seen as one of the most potent rebel groups fighting Assad's regime.