"All Muslims ought to be united against allthose who terrorize the innocents, and those who permit the killingof non-combatants without a justifiable reason.
"The Muslim soldier must perform his duty in this fight despitethe feeling of uneasiness of 'fighting without discriminating.' Hisintention must be to fight for enjoining of the truth and defeatingfalsehood. It's to prevent aggression on the innocents, or to apprehendthe perpetrators and bring them to justice. It's not his concern whatother consequences of the fighting that might result in his personaldiscomfort, since he alone can neither control it nor prevent it.Furthermore, all deeds are accounted (by God) according to theintentions.
"To sum up, it's acceptable-God willing-for the Muslim Americanmilitary personnel to partake in the fighting in the upcoming battles,against whomever their country decides has perpetrated terrorism againstthem. Keeping in mind to have the proper intention, as explained earlier,so no doubts would be cast about their loyalty to their country, or toprevent harm to befall them as might be expected. This is in accordancewith the Islamic jurisprudence rules, which state that necessities dictateexceptions, as well as the rule that says one may endure a small harm toavoid a much greater harm. And God the Most High is Most Knowledgeableand Most Wise."
Source: Islamic Center of Greater Toledo