In Islam, power cannot be used except to defend people’s rights. Muslims should support justice and peace everywhere. Muslim armies, by the same token, should aid the oppressed and help the victims of injustice irrespective of the latter’s race, religion or locality.
Sheikh `Abdul-Majeed Subh, a prominent Al-Azhar scholar, states: “First of all, I’d like to state that Islam can be epitomized in one word: The Truth. And this issue can be tackled in two points:
Regarding the first point, I can say that if the case is right and just, i.e. to remove oppression and to achieve the truth, then a Muslim army can ask for the help of a non-Muslim army only if the leadership and command are held by Muslims. Otherwise, it is totally prohibited.
As for the second point, I can say that originally a Muslim army is not allowed to help a non-Muslim army in attacking a Muslim one. But if the case is to remove the oppression of that Muslim army, then Muslims firstly should try themselves by all means to remove this oppression. If they fail, then they can help a non-Muslim army in removing this oppression and achieving the truth under one condition: that the leadership and the supreme command are held by Muslims, as indicated in the first point. Otherwise, it is totally prohibited.”