First of all, it should be crystal clear that Islam never sanctions brutality or aggression, for, as you mentioned, Islam is the religion of peace. It never allows mass destruction. Islam has laid down many restrictions to make war more human and moral.

Here, we would like to cite for you the statement made by Dr. Taha Jabir Al-`Alwani, President of the Graduate School of Islamic and Social Sciences and President of the Fiqh Council. It reads: “It is a well established fact that Islam considers all humanity as one family. Their God is One; they belong to the same father and mother. Whenever there’s any conflict among the family members, they should and must find the best solution to settle their conflict. They don’t have the right to fight each other unless they can’t find any other solution. That means that war is an exceptional position. No party has right to kill the other; they are all members of the same family.
Weapons of mass destruction like nuclear, chemical weapons, etc. are not permissible to be used against the other members of your family because by the nature of these weapons, you can’t differentiate between the innocent and the criminal. If we look at this, we wouldn’t allow any nuclear, chemical weapons, which would kill the innocent and the aggressor, especially from the Islamic point of view. Allah Almighty says in the Qur’an: “Nor take life – which Allah has made sacred – except for just cause. And if anyone is slain wrongfully, We have given his heir authority (to demand retaliation or to forgive): but let him not exceed bounds in the matter of taking life; for he is helped (by the law).”(Al-Isra’: 33)
When we agree that war is exceptional, that means we must look at it like medicine. You don’t have right to use more than the dosage prescribed by the physician.. If you take overdose, that may lead to another problem. This is why Islam has made forbidden for Muslims to kill women, children, religious people, the people who leave the war area seeking peace; Islam cares also for the environment: trees, water, animals, etc.

With this, we understand that possessing power and weapons of mass destruction is a test from Allah to humans, to see whether they will restrain themselves from using these weapons against innocent people who are also part of the human family.”

Shedding more light on this, Sheikh Faysal Mawlawi, deputy chairman of the European Council for Fatwa and Research, adds:

“We would like to say also that Islam cares much for keeping the environment clean and pure so that man can lead a better and healthy life free from any diseases or illnesses. However, in case these nuclear weapons are used against Muslims, it becomes permissible for Muslims to defend themselves using the same weapon. This is based on the words of Allah: “If ye punish, then punish with the like of that wherewith ye were afflicted.” (An-Nahl: 126) Besides, reciprocity is surely a principle known to all members of the international community. Again, we stress the fact that all problems are to be solved in a peaceful way. Once we have no other choice but to fight, we are to defend ourselves, children, women and lands.”

Almighty Allah knows best.