Muslims are prohibited from killing
Act of self defence is allow. But no killing of innocent children, woman and old folks. No carpet bombing, no hiroshima and nagasaki.
Take not life, which God has made sacred, except by way of justice and law: thus does He command you, that you may learn wisdom" (Koran 6:151)
"… that if anyone killed a person - unless it be for murder or for spreading mischief in the land - it would be as if he killed the whole people: and if any one saved a life, it would be as if he saved the life of the whole people. Then although there came to them Our messengers with clear signs, yet, even after that, many of them continued to commit excesses in the land" (5:32)