If the building contains military assets, this is a war and it is far game.
Rule 97. Human Shields
Geneva Convention III
Article 23, first paragraph, of the 1949 Geneva Convention III provides:
No prisoner of war may at any time be sent to, or detained in areas where he may be exposed to the fire of the combat zone, nor may his presence be used to render certain points or areas immune from military operations.
Geneva Convention IV
Article 28 of the 1949 Geneva Convention IV provides: “The presence of a protected persons may not be used to render certain points or areas immune from military operations.”