Israel says it was never authorised, the UN says it was.
Either way it is a breach of article 9 of the 1864 Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armies in the Field to attack aid workers bearing the Red Cross symbol.
Art. 9. The personnel charged exclusively with the removal, transportation, and treatment of the sick and wounded, as well as with the administration of sanitary formations and establishments, and the chaplains attached to armies, shall be respected and protected under all circumstances. If they fall into the hands of the enemy they shall not be considered as prisoners of war.
Art. 20. The personnel protected in virtue of the first paragraph of Article 9, and Articles 10 and 11, will wear attached to the left arm a brassard bearing a red cross on a white ground, which will be issued and stamped by competent military authority, and accompanied by a certificate of identity in the case of persons attached to the sanitary service of armies who do not have military uniform.